8-Channel, 1 MSPS, 10-Bit SAR ADC
AD7298-1
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©20102011 Analog Devices, Inc. All rights reserved.
FEATURES
10-bit SAR ADC
8 single-ended inputs
Channel sequencer functionality
Fast throughput of 1 MSPS
Analog input range: 0 V to 2.5 V
Temperature range: 40°C to +125°C
Specified for VDD of 2.8 V to 3.6 V
Logic voltage VDRIVE = 1.65 V to 3.6 V
Power-down current: <10 µA
Internal 2.5 V reference
Internal power-on reset
High speed serial interface SPI
20-lead LFCSP
FUNCTIONAL BLOCK DIAGRAM
10-BIT
SUCCESSIVE
APPROXIMATION
ADC
INPUT
MUX
T/H
V
DD
GND
PD/RST
SCLK
DOUT
DIN
CS
V
DRIVE
V
IN7
V
IN0
CONTROL
LOGIC
SEQUENCER
V
REF
BUFREF
AD7298-1
09321-001
Figure 1.
GENERAL DESCRIPTION
The AD7298-1 is a 10-bit, high speed, low power, 8-channel,
successive approximation ADC. The part operates from a single
3.3 V power supply and features throughput rates up to 1 MSPS.
The device contains a low noise, wide bandwidth track-and-hold
amplifier that can handle input frequencies in excess of 30 MHz.
The AD7298-1 offers a programmable sequencer, which enables
the selection of a preprogrammable sequence of channels for
conversion. The device has an on-chip, 2.5 V reference that can
be disabled to allow the use of an external reference.
The device offers a 4-wire serial interface compatible with SPI and
DSP interface standards.
The AD7298-1 uses advanced design techniques to achieve very
low power dissipation at high throughput rates. The part also
offers flexible power/throughput rate management options. The
part is offered in a 20-lead LFCSP package.
PRODUCT HIGHLIGHTS
1. Ideally Suited to Monitoring System Variables in a Variety
of Systems. This includes telecommunications, and process
and industrial control.
2. High Throughput Rate of 1 MSPS with Low Power
Consumption.
3. Eight Single-Ended Inputs with a Channel Sequencer. A
consecutive sequence of channels can be selected on which
the ADC cycles and converts.
AD7298-1
Rev. A | Page 2 of 24
TABLE OF CONTENTS
Features .............................................................................................. 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Product Highlights ........................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Timing Specifications .................................................................. 5
Absolute Maximum Ratings ............................................................ 6
Thermal Resistance ...................................................................... 6
ESD Caution .................................................................................. 6
Pin Configuration and Function Description .............................. 7
Typical Performance Characteristics ............................................. 9
Terminology .................................................................................... 12
Circuit Information ........................................................................ 13
Converter Operation .................................................................. 13
Analog Input ............................................................................... 13
VDRIVE ............................................................................................ 14
The Internal or External Reference .......................................... 14
Control Register .............................................................................. 15
Modes of Operation ....................................................................... 16
Traditional Multichannel Mode of Operation ........................ 16
Repeat Operation ....................................................................... 17
Power-Down Modes .................................................................. 18
Powering Up the AD7298-1 ...................................................... 19
Reset ............................................................................................. 19
Serial Interface ................................................................................ 20
Layout and Configuration ............................................................. 21
Outline Dimensions ....................................................................... 22
Ordering Guide .......................................................................... 22
REVISION HISTORY
1/11Rev. 0 to Rev. A
Removed Input Impedance Parameter .......................................... 3
Added Input Capacitance Parameter of 8 pF ................................ 3
Changes to Figure 10 ...................................................................... 10
Changed C1 Value to 8 pF in Analog Input Section
.................. 13
Changes to Figure 22 ...................................................................... 14
10/10Revision 0: Initial Version
AD7298-1
Rev. A | Page 3 of 24
SPECIFICATIONS
VDD = 2.8 V to 3.6 V, VDRIVE = 1.65 V to 3.6 V, fSAMPLE = 1 MSPS, fSCLK = 20 MHz, VREF = 2.5 V internal, TA = −40°C to +125°C, unless
otherwise noted.
Table 1.
Parameter Min Typ Max Unit Test Conditions/Comments
DYNAMIC PERFORMANCE fIN = 50 kHz sine wave
Signal-to-Noise Ratio (SNR)1 61 61.5 dB
Signal-to-Noise-(and-Distortion) Ratio (SINAD)2 61 61.5 dB
Total Harmonic Distortion (THD)2 −82 −75 dB
Spurious-Free Dynamic Range (SFDR) −83 −76 dB
Intermodulation Distortion (IMD) f
A = 40.1 kHz, fB = 41.5 kHz
Second-Order Terms −86 dB
Third-Order Terms −86 dB
Channel-to-Channel Isolation −90 dB fIN = 50 kHz, fNOISE = 60 kHz
SAMPLE AND HOLD
Aperture Delay3 12 ns
Aperture Jitter3 40 ps
Full Power Bandwidth 30 MHz At 3 dB
10 MHz At 0.1 dB
DC ACCURACY
Resolution 10 Bits
Integral Nonlinearity (INL)2 ±0.25 ±0.5 LSB
Differential Nonlinearity (DNL)2 ±0.3 ±0.5 LSB Guaranteed no missed codes to 10 bits
Offset Error2 ±0.5 ±1.125 LSB
Offset Error Matching2 ±0.625 ±1.125 LSB
Offset Temperature Drift 4 ppm/°C
Gain Error2 ±0.25 ±1 LSB
Gain Error Matching2 ±0.16 ±0.625 LSB
Gain Temperature Drift 0.5 ppm/°C
ANALOG INPUT
Input Voltage Ranges 0 VREF V
DC Leakage Current ±0.01 ±1 μA
Input Capacitance 32 pF When in track mode
8 pF When in hold mode
REFERENCE INPUT/OUTPUT
Reference Output Voltage4 2.4925 2.5 2.5075 V ±0.3% maximum at 25°C
Long-Term Stability 150 ppm For 1000 hours
Output Voltage Hysteresis 50 ppm
Reference Input Voltage Range 1 2.5 V
DC Leakage Current ±0.01 ±1 μA External reference applied to the VREF pin
VREF Output Impedance 1 Ω
VREF Temperature Coefficient 12 35 ppm/°C
VREF Noise 60 μV rms Bandwidth = 10 MHz
LOGIC INPUTS
Input High Voltage, VINH 0.7 × VDRIVE V
Input Low Voltage, VINL 0.3 × VDRIVE V
Input Current, IIN ±0.01 ±1 μA VIN = 0 V or VDRIVE
Input Capacitance, CIN3 3 pF
AD7298-1
Rev. A | Page 4 of 24
Parameter Min Typ Max Unit Test Conditions/Comments
LOGIC OUTPUTS
Output High Voltage, VOH VDRIVE − 0.3 V VDRIVE < 1.8
V
DRIVE − 0.2 V VDRIVE ≥ 1.8
Output Low Voltage, VOL 0.4 V
Floating State Leakage Current ±0.01 ±1 μA
Floating State Output Capacitance3 8 pF
CONVERSION RATE
Conversion Time 1 t2 + (16 × tSCLK) μs For VIN0 to VIN7 with one cycle latency
Track-and-Hold Acquisition Time2, 3 100 ns Full-scale step input
Throughput Rate 1 MSPS fSCLK = 20 MHz; for analog voltage
conversions, one cycle latency
POWER REQUIREMENTS Digital inputs = 0 V or VDRIVE
VDD 2.8 3 3.6 V
VDRIVE 1.65 3 3.6 V
ITOTAL5 V
DD = 3.6 V, VDRIVE = 3.6 V
Normal Mode (Operational) 5.8 6.4 mA
Normal Mode (Static) 4.1 4.6 mA
Partial Power-Down Mode 2.7 3.3 mA
Full Power-Down Mode 1 1.6 μA TA = −40°C to +25°C
10 μA TA = −40°C to +125°C
Power Dissipation6
Normal Mode (Operational) 17.4 19.2 mW VDD = 3 V, VDRIVE = 3 V
23 mW
Normal Mode (Static) 14.8 16.6 mW
Partial Power-Down Mode 9.8 11.9 mW
Full Power-Down Mode 3.6 5.8 μW TA = −40°C to +25°C
36 μW TA = −40°C to +125°C
1 All specifications expressed in decibels are referred to full-scale input FSR and tested with an input signal at 0.5 dB below full scale, unless otherwise specified.
2 See the Terminology section.
3 Sample tested during initial release to ensure compliance.
4 Refers to the VREF pin specified for 25°C.
5 ITOTAL is the total current flowing in VDD and VDRIVE.
6 Power dissipation is specified with VDD = VDRIVE = 3.6 V, unless otherwise noted.
AD7298-1
Rev. A | Page 5 of 24
TIMING SPECIFICATIONS
VDD = 2.8 V to 3.6 V, VDRIVE = 1.65 V to 3.6 V, VREF = 2.5 V internal, TA = −40°C to +125°C, unless otherwise noted. Sample tested during
initial release to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VDRIVE) and timed from a voltage level
of 1.6 V.
Table 2.
Parameter Limit at TMIN, TMAX Unit Test Conditions/Comments
tCONVERT t2 + (16 × tSCLK) µs max Conversion time
820 ns typ Each ADC channel VIN0 to VIN7, fSCLK = 20 MHz
fSCLK1 50 kHz min Frequency of external serial clock
20 MHz max Frequency of external serial clock
tQUIET 6 ns min Minimum quiet time required between the end of the serial read and the start of
the next voltage conversion in repeat and nonrepeat mode.
t2 10 ns min CS to SCLK setup time
t31 15 ns max Delay from CS (falling edge) until DOUT three-state disabled
t41 Data access time after SCLK falling edge
35 ns max VDRIVE = 1.65 V to 3 V
28 ns max VDRIVE = 3 V to 3.6 V
t5 0.4 × tSCLK ns min SCLK low pulse width
t6 0.4 × tSCLK ns min SCLK high pulse width
t71 14 ns min SCLK to DOUT valid hold time
t81 16/34 ns min/ns max SCLK falling edge to DOUT high impedance
t9 5 ns min DIN setup time prior to SCLK falling edge
t
10
4 ns min DIN hold time after SCLK falling edge
t111 30 ns max Delay from CS rising edge to DOUT high impedance
tPOWER-UP 6 ms max Internal reference power-up time from full power-down
1 Measured with a load capacitance on DOUT of 15 pF.
AD7298-1
Rev. A | Page 6 of 24
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Rating
VDD to GND, GND1 0.3 V to +5 V
VDRIVE to GND, GND1 0.3 V to + 5 V
Analog Input Voltage to GND1 −0.3 V to +3 V
Digital Input Voltage to GND −0.3 V to V
DRIVE
+ 0.3 V
Digital Output Voltage to GND −0.3 V to VDRIVE + 0.3 V
VREF to GND1 −0.3 V to +3 V
AGND to GND −0.3 V to +0.3 V
Input Current to Any Pin Except Supplies ±10 mA
Operating Temperature Range −40°C to +125°C
Storage Temperature Range −65°C to +150°C
Junction Temperature 150°C
Pb-free Temperature, Soldering
Reflow 260(0)°C
ESD 3.5 kV
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL RESISTANCE
Table 4. Thermal Resistance
Package Type θ
JA
θ
JC
Unit
20-Lead LFCSP 52 6.5 °C/W
ESD CAUTION
AD7298-1
Rev. A | Page 7 of 24
PIN CONFIGURATION AND FUNCTION DESCRIPTION
Figure 2. Pin Configuration
Table 5. Pin Function Descriptions
Pin No. Mnemonic Description
1 to 5,
18 to 20
VIN3, VIN4
VIN5, VIN6,
VIN7, VIN0,
V
IN1
, V
IN2
Analog Inputs. The AD7298-1 has eight single-ended analog inputs that are multiplexed into the on-chip track-
and-hold. Each input channel can accept analog inputs from 0 V to 2.5 V. Any unused input channels should be
connected to GND1 to avoid noise pickup.
6 GND1 Ground. Ground reference point for the internal reference circuitry on the AD7298-1. The external reference
signals and all analog input signals should be referred to the GND1 voltage. The GND1 pin should be connected
to the ground plane of a system. All ground pins should ideally be at the same potential and must not be more
than 0.3 V apart, even on a transient basis. The VREF pin should be decoupled to this ground pin via a 10 µF
decoupling capacitor.
7 VREF
Internal Reference/External Reference Supply. The nominal internal reference voltage of 2.5 V appears at this pin.
Provided the output is buffered, the on-chip reference can be taken from this pin and applied externally to the
rest of a system. Decoupling capacitors should be connected to this pin to decouple the reference buffer. For
best performance, it is recommended to use a 10 µF decoupling capacitor on this pin to GND1. The internal
reference can be disabled and an external reference supplied to this pin, if required. The input voltage range for
the external reference is 2.0 V to 2.5 V.
8 DCAP Decoupling Capacitor Pins. Decoupling capacitors (1 µF recommended) are connected to this pin to decouple
the internal LDO.
9 GND Ground. Ground reference point for all analog and digital circuitry on the AD7298-1. The GND pin should be
connected to the ground plane of the system. All ground pins should ideally be at the same potential and must
not be more than 0.3 V apart, even on a transient basis. Both the DCAP and VDD pins should be decoupled to this
GND pin.
10 VDD Supply Voltage, 2.8 V to 3.6 V. This supply should be decoupled to GND with 10 µF and 100 nF decoupling capacitors.
11 CS Chip Select, Active Low Logic Input. This pin is edge triggered on the falling edge of this input, the track-and-
hold goes into hold mode, and a conversion is initiated. This input also frames the serial data transfer. When CS is
low, the output bus is enabled and the conversion result becomes available on the DOUT output.
12 NC No Connect.
13 DIN Data In, Logic Input. Data to be written to the AD7298-1 control register is provided on this input and is clocked
into the register on the falling edge of SCLK.
14 DOUT Serial Data Output. The conversion result from the AD7298-1 is provided on this output as a serial data stream.
The bits are clocked out on the falling edge of the SCLK input. The data stream from the AD7298-1 consists of
four address bits indicating which channel the conversion result corresponds to, followed by the 10 bits of
conversion data (MSB first).
15 SCLK Serial Clock, Logic Input. A serial clock input provides the SCLK for accessing the data from the AD7298-1.
AD7298-1
Rev. A | Page 8 of 24
Pin No. Mnemonic Description
16 VDRIVE Logic Power Supply Input. The voltage supplied at this pin determines the voltage at which the interface
operates. This pin should be decoupled to ground. The voltage range on this pin is 1.65 V to 3.6 V and may be less
than the voltage at VDD but should never exceed it by more than 0.3 V.
17 PD/RST Power-Down Pin. This pin places the part into full power-down mode and enables power conservation when operation
is not required. This pin can be used to reset the device by toggling the pin low for a minimum of 1 ns and a maximum
of 100 ns. If the maximum time is exceeded, the part enters power-down mode. When placing the AD7298-1 into full
power-down mode, the analog inputs must return to 0 V.
EPAD The exposed metal paddle on the bottom of the LFCSP package should be soldered to PCB ground for proper
functionality and heat dissipation.
AD7298-1
Rev. A | Page 9 of 24
TYPICAL PERFORMANCE CHARACTERISTICS
–110
–90
–70
–50
–30
–100
–80
–60
–40
–20
–10
0
0100 200 300
FREQUENCY (MHz)
SIGNAL POWER (dB)
400 500 600
V
DD
= V
DRIVE
= 3V
f
SAMPLE
= 1.17647M Hz
f
IN
= 50kHz
f
SCLK
= 20MHz
SNR = 61. 83dB
THD = –80.23dB
09321-047
Figure 3. Typical FFT
–1.0
–0.8
–0.6
0.6
0.4
0.2
0
0.2
0.4
0.8
1.0
1101 201 301 401 501 601 701 801 901 1001
INL (LSB)
CODE
V
DD
= 3V
V
DRIVE
= 3V
09321-040
Figure 4. Typical ADC INL
–1.0
–0.8
–0.6
–0.4
0.6
0.4
0.2
0
0.2
0.8
1.0
1101 201 301 401 501 601 701 801 901 1001
DNL ( LSB)
CODE
VDD = 3V
VDRIVE = 3V
09321-041
Figure 5. Typical ADC DNL
–0.50
–0.40
–0.30
–0.20
–0.10
0
0.10
0.20
0.30
0.40
0.50
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
INL (LSB)
VREF (V)
INL (Positive)
INL (Negat ive)
09321-038
Figure 6. INL vs. VREF
–0.50
–0.40
–0.30
–0.20
–0.10
0
0.10
0.20
0.30
0.40
0.50
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
DNL (LSB)
V
REF
(V)
INL (Positive)
INL (Negat ive)
09321-039
Figure 7. DNL vs. VREF
2
3
4
5
6
7
8
9
10
11
00.5 1.0 1.5 2.0 2.5
EFFECTIVE NUMBER OF BITS
EXTERNAL VOLTAGE REFERENCE (V)
V
DD
= 3V
V
DRIVE
= 3V
09321-042
Figure 8. Effective Number of Bits vs. VREF
AD7298-1
Rev. A | Page 10 of 24
1.0
1.5
2.0
2.5
3.0
00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
CURRENT LOAD ( mA)
V
REF
(V)
V
DD
= V
DRIVE
= 3V
09321-109
Figure 9. VREF vs. Reference Output Current Drive
–110
–108
–106
–104
–102
–100
–98
–96
–94
–92
–90
1k 10k 100k 1M 10M 100M
PSRR (dB)
RIPPLE FREQUENCY (Hz)
V
DD
= 3V
V
DRIVE
= 3V
09321-110
Figure 10. PSRR vs. Supply Ripple Frequency Without Supply Decoupling
70
75
80
85
90
95
100
105
110
050 100 150 200 250 300 350 400 450 500 550
ISOLATION (dB)
fNOISE
(kHz)
09321-111
Figure 11. Channel-to-Channel Isolation, fIN = 50 kHz
58.0
58.5
59.0
59.5
60.0
60.5
61.0
61.5
62.0
10 100
SI NAD ( dB)
INP UT FREQUENCY (kHz )
V
DD
= 3V
V
DRIVE
= 3V
R
SOURCE
= 0
R
SOURCE
= 10
R
SOURCE
= 33
R
SOURCE
= 47
R
SOURCE
= 100
R
SOURCE
= 200
09321-046
Figure 12. SINAD vs. Analog Input Frequency for Various Source Impedances
60.50
60.75
61.00
61.25
61.50
61.75
62.00
1.0 1.5 2.0 2.5
SI NAD ( dB)
EXTERNAL REFERENCE VOLTAGE (V)
VDD = 3V
VDRIVE = 3V
09321-043
Figure 13. SINAD vs. Reference Voltage
–90
–89
–88
–87
–86
–85
–84
–83
–82
–81
–80
1.0 1.5 2.0 2.5
THD ( dB)
EXTERNAL REFERENCE VOLTAGE (V)
VDD = 3V
VDRIVE = 3V
09321-044
Figure 14. THD vs. Reference Voltage
AD7298-1
Rev. A | Page 11 of 24
–90
–85
–80
–75
–70
–65
–60
10 100
THD ( dB)
INP UT FREQUENCY (kHz )
V
DD
= 3V
V
DRIVE
= 3V
R
SOURCE
= 0
R
SOURCE
= 10
R
SOURCE
= 33
R
SOURCE
= 47
R
SOURCE
= 100
R
SOURCE
= 200
09321-045
Figure 15. THD vs. Analog Input Frequency for Various Source Impedances
0
1
2
3
4
5
6
0200 400 600 800 1000 1200
CURRENT ( mA)
THROUGHPUT (kSP S )
V
DD
CURRENT
V
DRIVE
CURRENT
09321-114
V
DD
= V
DRIVE
= 3V
Figure 16. Average Supply Current vs. Throughput Rate
10
11
12
13
14
15
16
17
18
19
0100 200 300 400 500 600 700 800 900 1000
POWER (mW)
THROUGHPUT (kSP S )
V
DD
= V
DRIVE
= 3V
09321-118
Figure 17. Power vs. Throughput in Normal Mode with VDD = 3 V
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6
TOTAL CURRENT (µA)
VDD (V)
–40°C
0°C
+25°C
VDRIVE = 3V
+85°C
+105°C
+125°C
09321-119
Figure 18. Full Shutdown Current vs. Supply Voltage for Various
Temperatures
AD7298-1
Rev. A | Page 12 of 24
TERMINOLOGY
Signal-to-Noise-and-Distortion Ratio (SINAD)
The measured ratio of signal-to-noise and distortion at the
output of the ADC. The signal is the rms amplitude of the
fundamental. Noise is the sum of all nonfundamental signals up
to half the sampling frequency (fS/2), excluding dc. The ratio is
dependent on the number of quantization levels in the digitization
process; the more levels, the smaller the quantization noise. The
theoretical signal-to-noise-and-distortion ratio for an ideal N-
bit converter with a sine wave input is given by
Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB
Thus, the SINAD is 61.96 dB for an ideal 10-bit converter.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
the AD7298-1, it is defined as
1
2
6
2
5
2
4
2
3
2
2
log20)dB( V
VVVVV
THD
++++
=
where:
V1 is the rms amplitude of the fundamental.
V2, V3, V4, V5, and V6 are the rms amplitudes of the second
through sixth harmonics.
Peak Harmonic or Spurious Noise
The ratio of the rms value of the next largest component in the
ADC output spectrum (up to fS/2 and excluding dc) to the rms
value of the fundamental. Typically, the value of this specification
is determined by the largest harmonic in the spectrum, but for
ADCs where the harmonics are buried in the noise floor, it is a
noise peak.
Integral Nonlinearity
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. The endpoints are
zero scale, a point 1 LSB below the first code transition, and full
scale, a point 1 LSB above the last code transition.
Differential Nonlinearity
The difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset Error
The deviation of the first code transition (00…000) to
(00…001) from the idealthat is, GND1 + 1 LSB.
Offset Error Matching
The difference in offset error between any two channels.
Gain Error
The deviation of the last code transition (111…110) to
(111…111) from the ideal (that is, VREF − 1 LSB) after the offset
error has been adjusted out.
Gain Error Matching
The difference in gain error between any two channels.
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode at the end
of the conversion. The track-and-hold acquisition time is the
time required for the output of the track-and-hold amplifier to
reach its final value, within ±1 LSB, after the end of the conversion.
Power Supply Rejection Ratio (PSRR)
PSRR is defined as the ratio of the power in the ADC output at
full-scale frequency, f, to the power of a 100 mV p-p sine wave
applied to the ADC VDD supply of frequency, fS. The frequency
of the input varies from 5 kHz to 25 MHz.
PSRR (dB) = 10 log(Pf/PfS)
where:
Pf is the power at frequency, f, in the ADC output.
PfS is the power at frequency, fS, in the ADC output.
AD7298-1
Rev. A | Page 13 of 24
CIRCUIT INFORMATION
The AD7298-1 is a high speed, 8-channel, 10-bit ADC. The part
can be operated from a 2.8 V to 3.6 V supply and is capable of
throughput rates of 1 MSPS per analog input channel.
The AD7298-1 provides the user with an on-chip, track-and-hold
ADC and a serial interface housed in a 20-lead LFCSP. The
AD7298-1 has eight, single-ended input channels with channel
repeat functionality, which allows the user to select a channel
sequence through which the ADC can cycle with each consecutive
CS falling edge. The serial clock input accesses data from the
part, controls the transfer of data written to the ADC, and
provides the clock source for the successive approximation
ADC. The analog input range for the AD7928-1 is 0 V to VREF.
The AD7298-1 operates with one cycle latency, which means
that the conversion result is available in the serial transfer
following the cycle in which the conversion is performed.
The AD7298-1 provides flexible power management options to
allow the user to achieve the best power performance for a given
throughput rate. These options are selected by programming
the partial power-down bit, PPD, in the control register and
using the PD/RST pin.
CONVERTER OPERATION
The AD7298-1 is a 10-bit successive approximation ADC based
around a capacitive DAC. Figure 19 and Figure 20 show simplified
schematics of the ADC. The ADC is comprised of control logic,
SAR, and a capacitive DAC that are used to add and subtract
fixed amounts of charge from the sampling capacitor to bring
the comparator back into a balanced condition. Figure 19 shows
the ADC during its acquisition phase. SW2 is closed and SW1 is
in Position A. The comparator is held in a balanced condition
and the sampling capacitor acquires the signal on the selected
VIN channel.
CONTROL
LOGIC
CAPACITIVE
DAC
V
IN
A
B
SW1 SW2
GND1 COMPARATOR
08754-004
Figure 19. ADC Acquisition Phase
When the ADC starts a conversion (see Figure 20), SW2 opens
and SW1 moves to Position B, causing the comparator to become
unbalanced. The control logic and the capacitive DAC are used to
add and subtract fixed amounts of charge to bring the comparator
back into a balanced condition. When the comparator is
rebalanced, the conversion is complete. The control logic
generates the ADC output code. Figure 22 shows the transfer
function of the ADC.
CONTROL
LOGIC
CAPACITIVE
DAC
V
IN
A
B
SW1 SW2
GND1 COMPARATOR
09321-005
Figure 20. ADC Conversion Phase
ANALOG INPUT
Figure 21 shows an equivalent circuit of the analog input structure
of the AD7298-1. The two diodes, D1 and D2, provide ESD
protection for the analog inputs. Care must be taken to ensure
that the analog input signal never exceeds the internally generated
LDO voltage of 2.5 V (DCAP) by more than 300 mV. This causes
the diodes to become forward-biased and to start conducting
current into the substrate. The maximum current these diodes
can conduct without causing irreversible damage to the part is
10 mA. Capacitor C1, in Figure 21, is typically about 8 pF and
can primarily be attributed to pin capacitance. The R1 resistor is
a lumped component made up of the on resistance of a switch
(track-and-hold switch) and includes the on resistance of the
input multiplexer. The total resistance is typically about 155 Ω.
The capacitor, C2, is the ADC sampling capacitor and has a
capacitance of 34 pF typically.
C1
pF
C2
pF
R1
D2 CONVERSION PHASE: SWITCH OPEN
TRACK PHAS E : SWI TCH CLOSED
D1
DCAP (2.5V)
VIN
09321-006
Figure 21. Equivalent Analog Input Circuit
For ac applications, removing high frequency components from
the analog input signal is recommended by using an RC low-pass
filter on the relevant analog input pin. In applications where
harmonic distortion and signal-to-noise ratios are critical, the
analog input should be driven from a low impedance source. Large
source impedances significantly affect the ac performance of the
ADC. This may necessitate the use of an input buffer amplifier.
The choice of the op amp is a function of the particular application
performance criteria.
AD7298-1
Rev. A | Page 14 of 24
ADC Transfer Function
The output coding of the AD7298-1 is straight binary for the
analog input channel conversion results. The designed code
transitions occur at successive LSB values (that is, 1 LSB, 2 LSBs,
and so forth). The LSB size is VREF/1024 for the AD7298-1. The
ideal transfer characteristic for the AD7298-1 for straight binary
coding is shown in Figure 22.
111...111
111...110
111...000
011...111
000...010
000...001
000...000
1LSB = V
REF
/1024
ANALOG INPUT
NOTES
1. V
REF
IS 2.5V.
ADC CODE
+V
REF
1LSB1LSB
0V
09321-007
Figure 22. Straight Binary Transfer Characteristic
VDRIVE
The AD7298-1 also provides the VDRIVE feature. VDRIVE controls
the voltage at which the serial interface operates. VDRIVE allows
the ADC to easily interface to both 1.8 V and 3 V processors.
For example, if the AD7298-1 were operated with a VDD of
3.3 V, t h e V DRIVE pin could be powered from a 1.8 V supply.
This enables the AD7298-1 to operate with a larger dynamic
range with a VDD of 3.3 V while still being able to interface to
1.8 V processors. Take care to ensure VDRIVE does not exceed
VDD by more than 0.3 V (see the Absolute Maximum Ratings
section).
THE INTERNAL OR EXTERNAL REFERENCE
The AD7298-1 can operate with either the internal 2.5 V on-chip
reference or an externally applied reference. The EXT_REF bit
in the control register is used to determine whether the internal
reference is used. If the EXT_REF bit is selected in the control
register, an external reference can be supplied through the VREF
pin. At power-up, the internal reference is enabled. Suitable
external reference sources for the AD7298-1 include AD780,
AD1582, ADR431, REF193, and ADR391.
The internal reference circuitry consists of a 2.5 V band gap
reference and a reference buffer. When the AD7298-1 is operated
in internal reference mode, the 2.5 V internal reference is
available at the VREF pin, which should be decoupled to GND1
using a 10 µF capacitor. It is recommended that the internal
reference be buffered before applying it elsewhere in the system.
The internal reference is capable of sourcing up to 2 mA of current
when the converter is static. The reference buffer requires 5.5 ms to
power up and charge the 10 µF decoupling capacitor during the
power-up time.
AD7298-1
Rev. A | Page 15 of 24
CONTROL REGISTER
The control register of the AD7298-1 is a 16-bit, write-only
register. Data is loaded from the DIN pin of the AD7298-1 on
the falling edge of SCLK. The data is transferred on the DIN
line at the same time that the conversion result is read from the
part. The data transferred on the DIN line corresponds to the
AD7298-1 configuration for the next conversion. This requires
16 serial clocks for every data transfer. Only the information
provided on the first 16 falling clock edges (after the falling
edge of CS) is loaded to the control register. MSB denotes the
first bit in the data stream. The bit functions are outlined in
Table 6 and Table 7. At power-up, the default content of the
control register is all zeros.
Table 6. Control Register Bit Functions
MSB LSB
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
WRITE REPEAT CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 0 DONTC DONTC EXT_REF DONTC PPD
Table 7. Control Register Bit Function Description
Bit Mnemonic Description
D15 WRITE The value written to this bit determines whether the subsequent 15 bits are loaded to the control register. If this
bit is a 1, the following 15 bits are written to the control register. If this bit is a 0, then the remaining 15 bits are not
loaded to the control register, and it remains unchanged.
D14 REPEAT This bit enables the repeated conversion of the selected sequence of channels.
D13 to
D6
CH0 to
CH7
These eight channel selection bits are loaded at the end of the current conversion and select which analog input
channel is to be converted in the next serial transfer, or they can select the sequence of channels for conversion in
the subsequent serial transfers. Each CHx bit corresponds to an analog input channel. A channel or sequence of
channels is selected for conversion by writing a 1 to the appropriate CHx bit/bits. Channel address bits
corresponding to the conversion result are output on DOUT prior to the 10 bits of data. The next channel to be
converted is selected by the mux on the 14th SCLK falling edge.
D5 0 Zero should be written to this bit.
D4, D3,
D1
DONTC Don’t care.
D2 EXT_REF Writing Logic 1 to this bit, enables the use of an external reference. The input voltage range for the external
reference is 1 V to 2.5 V. The external reference should not exceed 2.5 V or the device performance is affected.
D0 PPD This partial power-down mode is selected by writing a 1 to this bit in the control register. In this mode, some of
the internal analog circuitry is powered down. The AD7298-1 retains the information in the control register while
in partial power-down mode. The part remains in this mode until a 0 is written to this bit.
Table 8. Channel Address Bits
ADD3 ADD2 ADD1 ADD0 Analog Input Channel
0 0 0 0 VIN0
0 0 0 1 VIN1
0 0 1 0 VIN2
0 0 1 1 VIN3
0 1 0 0 V
IN4
0 1 0 1 VIN5
0 1 1 0 VIN6
0 1 1 1 VIN7
AD7298-1
Rev. A | Page 16 of 24
MODES OF OPERATION
The AD7298-1 offers different modes of operation that are
designed to provide additional flexibility for the user. These
options can be chosen by programming the content of the
control register to select the desired mode.
TRADITIONAL MULTICHANNEL MODE OF
OPERATION
The AD7298-1 can operate as a traditional multichannel ADC,
where each serial transfer selects the next channel for conversion.
One must write to the control register to configure and select
the desired input channel prior to initiating any conversions. In
the traditional mode of operation, the CS signal is used to frame
the first write to the converter on the DIN pin. In this mode of
operation, the REPEAT bit in the control register is set to a low
logic level (0), therefore the REPEAT function is not in use. The
data, which appears on the DOUT pin during the initial write to
the control register, is invalid. The first CS falling edge initiates a
write to the control register to configure the device; a conversion is
then initiated for the selected analog input channel (VIN0) on the
subsequent (second) CS falling edge; and the third CS falling edge
will have the result (VIN2) available for reading. The AD7298-1
operates with one cycle latency, therefore the conversion result
corresponding to each conversion is available one serial read
cycle after the cycle in which the conversion was initiated.
As the device operates with one cycle latency, the control
register configuration sets up the configuration for the next
conversion, which is initiated on the next CS falling edge, but
the first bit of the corresponding result is not clocked out until
the subsequent falling CS edge, as shown in Figure 23.
If more than one channel is selected in the control register, the
AD7298-1 converts all selected channels sequentially in ascending
order on successive CS falling edges. Once all the selected channels
in the control register are converted, the AD7298-1 ceases converting
until the user rewrites to the control register to select the next
channel for conversion. This operation is shown in Figure 24.
DOUT returns all 1s if the sequence of conversions is completed or
if no channel is selected.
CS
SCLK
DOUT
DIN
110 16 116 116 116
CONVE RSIO N RESUL T
FO R CHANNEL 4
CONVE RSIO N RESUL T
FO R CHANNEL 1
INVAL ID DATAINV ALID DATA
DATA WRITTEN T O CONT ROL
REGISTER CHANNE L 4 SEL ECTE D
DATA WRITTEN T O CONT ROL
REGISTER CHANNE L 1 SEL ECTE D NO W RITE T O THE
CONT ROL REG ISTER
NO W RITE T O THE
CONT ROL REG ISTER
09321-009
Figure 23. Configuring a Conversion and Read with the AD7298-1, One Channel Selected for Conversion
CS
SCLK
DOUT
DIN
110 16 116 116
CONVE RSIO N RESUL T
FO R CHANNEL 1
CONVE RSIO N RESUL T
FO R CHANNEL 5
CONVE RSIO N RESUL T
FO R CHANNEL 2
INVAL ID DATAINVAL ID DATA
NO W RITE T O THE
CONT ROL REG ISTER
NO W RITE T O THE
CONT ROL REG ISTER
NO W RITE T O THE
CONT ROL REG ISTER
DATA WRITTEN T O CO NTROL
REGISTER CH 1 AND 2 SEL ECTE D
CS
SCLK
DOUT
DIN
116 116
DATA WRITTEN T O CO NTROL
REGISTER CHANNE L 5 SEL ECTE D
09321-010
Figure 24. Configuring a Conversion and Read with the AD7298-1, Numerous Channels Selected for Conversion
AD7298-1
Rev. A | Page 17 of 24
CS
SCLK
DOUT
DIN
110 16 116 116
CONVE RSIO N RESUL T
FO R CHANNEL 0
CONVE RSIO N RESUL T
FO R CHANNEL 1
INVAL ID DATAINVALID DATA
NO W RITE T O THE
CONT ROL REG ISTER NO W RITE TO THE
CONT ROL REG ISTER
DATA WRITTEN T O CO NTROL
REGISTER CH0 , CH1, AND CH2
SELECTED: REPEAT = 1
CS
SCLK
DOUT
DIN
116 116 116
CONVE RSIO N RESUL T
FO R CHANNEL 0
CONVE RSIO N RESUL T
FO R CHANNEL 2
NO W RITE T O THE
CONT ROL REG ISTER NO W RITE TO THE
CONT ROL REG ISTER
NO W RITE T O THE
CONT ROL REG ISTER
09321-011
Figure 25. Configuring a Conversion and Read in Repeat Mode
REPEAT OPERATION
The REPEAT bit in the control register allows the user to select
a sequence of channels on which the AD7298-1 continuously
converts. When the REPEAT bit is set in the control register, the
AD7298-1 continuously cycles through the selected channels in
ascending order, beginning with the lowest channel and converting
all channels selected in the control register. On completion of
the sequence, the AD7298-1 returns to the first selected channel
in the control register and recommences the sequence.
The conversion sequence of the selected channels in the repeat
mode of operation continues until the control register of the
AD7298-1 is reprogrammed. It is not necessary to write to the
control register once a repeat operation is initiated unless a change
in the AD7298-1 configuration is required. The WRITE bit
must be set to zero, or the DIN line tied low to ensure that the
control register is not accidentally overwritten or the automatic
conversion sequence interrupted.
A write to the control register during the repeat mode of operation
resets the cycle even if the selected channels are unchanged.
Thus, the next conversion by the AD7298-1 after a write
operation will be the first selected channel in the sequence.
To select a sequence of channels, the associated channel bit
must be set to a logic high state (1) for each analog input whose
conversion is required. For example, if the REPEAT bit = 1, then
CH0, CH1, and CH2 = 1. The VIN0 analog input is converted on
the first CS falling edge following the write to the control register,
the VIN1 channel is converted on the subsequent CS falling edge,
and the VIN0 conversion result is available for reading. The third
CS falling edge following the write operation initiates a conversion
on VIN2 and has the VIN1 result available for reading. The AD7298-1
operates with one cycle latency, therefore the conversion result
corresponding to each conversion is available one serial read
cycle after the cycle in which the conversion is initiated.
This mode of operation simplifies the operation of the device by
allowing consecutive channels to be converted without having
to reprogram the control register or write to the part on each
serial transfer. Figure 25 illustrates how to set up the AD7298-1
to continuously convert on a particular sequence of channels.
To exit the repeat mode of operation and revert to the traditional
mode of operation of a multichannel ADC, ensure that the
REPEAT bit = 0 on the next serial write.
AD7298-1
Rev. A | Page 18 of 24
POWER-DOWN MODES
The AD7298-1 has a number of power conservation modes of
operation that are designed to provide flexible power management
options. These options can be chosen to optimize the power
dissipation/throughput rate ratio for different application
requirements. The power-down modes of operation of the
AD7298-1 are controlled by the power-down (PPD) bit in the
control register and the PD/RST pin on the device. When power
supplies are first applied to the AD7298-1, care should be taken
to ensure that the part is placed in the required mode of operation.
Normal Mode
Normal mode is intended for the fastest throughput rate
performance because the user does not have to be concerned
about any power-up times since the AD7298-1 remains fully
powered on at all times. Figure 26 shows the general diagram
of the normal mode operation of the AD7298-1. The conversion
is initiated on the falling edge of CS and the track-and-hold enters
hold mode. On the 14th SCLK falling edge, the track-and-hold
returns to track mode and starts acquiring the analog input, as
described in the Serial Interface section. The data presented to
the AD7298-1 on the DIN line during the first 16 clock cycles of
the data transfer are loaded into the control register (provided the
WRITE bit is 1). The part remains fully powered up in normal
mode at the end of the conversion as long as the PPD bit is set
to 0 in the write transfer during that conversion.
To ensure continued operation in normal mode, the PPD bit
should be loaded with 0 on every data write operation. Sixteen
serial clock cycles are required to complete the conversion and
access the conversion result. For specified performance, the
throughput rate should not exceed 1 MSPS. When a conversion
is complete and the CS has returned high, a minimum of the quiet
time, tQUIET, must elapse before bringing CS low again to initiate
another conversion and access the previous conversion result.
CS
SCLK
DOUT
DIN
116
DATA WRITTEN T O CONT ROL
REGISTER IF REQUI RED
4 CHANNEL ADDRESS BITS
+ CONVERSION RE SULT
09321-012
Figure 26. Normal Mode Operation
Partial Power-Down Mode
In this mode, part of the internal circuitry on the AD7298-1
is powered down. The AD7298-1 enters partial power-down
on the CS rising edge once the current serial write operation
containing 16 SCLK clock cycles is completed. To enter partial
power-down, the PPD bit in the control register should be set to
1 on the last required read transfer from the AD7298-1. Once in
partial power-down mode, the AD7298-1 transmits all 1s on the
DOUT pin if CS is toggled low.
The AD7298-1 remains in partial power-down until the power-
down bit, PPD, in the control register is changed to Logic Level 0.
The AD7298-1 begins powering up on the rising edge of CS
following the write to the control register disabling the power-
down bit. Once tQUIET has elapsed, a full 16 SCLK writes to the
control register must be completed to update its content with
the desired channel configuration for the subsequent conversion.
A valid conversion is then initiated on the next CS falling edge.
Because the AD7298-1 has one cycle latency, the first conversion
result after exiting partial power-down mode is available in the
fourth serial transfer, as shown in Figure 27. The first cycle updates
the PPD bit, the second cycle updates the configuration and
Channel ID bits, the third completes the conversion, and the
fourth accesses the DOUT valid result. The use of this mode
enables a reduction in the overall power consumption of the device.
Full Power-Down Mode
In this mode, all internal circuitry on the AD7298-1 is powered
down, and no information is retained in the control register or any
other internal register.
The AD7298-1 is placed into full power-down mode by bringing
the logic level on the PD/RST pin low for greater than 100 ns.
When placing the AD7298-1 in full power-down mode, the ADC
inputs must return to 0 V. The PD/RST pin is asynchronous to the
clock; therefore, it can be triggered at any time. The part can be
powered up for normal operation by bringing the PD/RST pin
logic level back to a high logic state.
The full power-down feature can be used to reduce the average
power consumed by the AD7298-1 when operating at lower
throughput rates. The user should ensure that tPOWER-UP has
elapsed prior to programming the control register and initiating
a valid conversion.
CS
SCLK
DOUT
DIN
110 16 116 116
INVAL ID DATA INVAL ID DATA
WRI T E T O THE CO NT ROL
REGISTER, SEL ECT CH1, PPD = 0
PART I S IN
PARTIAL
POWER DO W N
WRI T E T O CO NTROL
REGISTER, PPD = 0.
CONT ROL REG ISTER CONFIG URED
TO POWER UP DEVI CE. SELECT ANALOG INPUT CHANNEL S
FO R CONVERSI ON. T HE NEXT CYCL E
WI L L CONVERT T HE F IRST CHANNEL
PROGRAM MED I N T HIS WRITE OPERATI ON.
PART BEG INS TO
POWER UP O N CS
RISING EDGE.
THE PART IS FULLY
POWERED UP O NCE THE
WRI T E T O THE CO NT ROL
REGISTER IS COMPL ETED.
AD7298 CONVERTING CHANNEL 1
NEXT CYCLE HAS CHANNE L 1
RESULT AVAILABLE F OR READI NG.
t
QUIET
t
QUIET
09321-213
NO W RITE T O
CONT ROL REG ISTER
Figure 27. Partial Power-Down Mode of Operation
AD7298-1
Rev. A | Page 19 of 24
POWERING UP THE AD7298-1
The AD7298-1 contains a power-on reset circuit that sets the
control register to its default setting of all zeros; therefore, the
internal reference is enabled and the device is configured for the
normal mode of operation. At power-up, the internal reference is
by default enabled, which takes up to 6 ms (maximum) to power up.
If an external reference is being used, the user does not need to
wait for the internal reference to power up fully. The AD7298-1
digital interface is fully functional after 500 µs from the initial
power-up. Therefore, the user can write to the control register
after 500 µs to switch to external reference mode. The AD7298-1 is
then immediately ready to convert once the external reference is
available on the VREF pin.
When supplies are first applied to the AD7298-1, the user must
wait the specified 500 µs before programming the control register
to select the desired channels for conversion.
RESET
The AD7298-1 includes a reset feature that can be used to reset
the device and the contents of all internal registers, including
the control register, to their default state.
To activate the reset operation, the PD/RST pin should be brought
low for no longer than 100 ns. It is asynchronous with the clock;
therefore, it can be triggered at any time. If the PD/RST pin is
held low for greater than 100 ns, the part enters full power-down
mode. It is imperative that the PD/RST pin be held at a stable
logic level at all times to ensure normal operation.
AD7298-1
Rev. A | Page 20 of 24
SERIAL INTERFACE
Figure 28 shows the detailed timing diagram for the serial interface
to the AD7298-1. The serial clock provides the conversion clock
and controls the transfer of information to and from the AD7298-1
during each conversion.
The CS signal initiates the data transfer and conversion process.
The falling edge of CS puts the track-and-hold into hold mode
at which point the analog input is sampled and the bus is taken
out of three-state. The conversion is also initiated at this point
and requires 16 SCLK cycles to complete. The track-and-hold
goes back into track mode on the 14th SCLK falling edge as shown
in Figure 28 at Point B. On the 16th SCLK falling edge or on the
rising edge of CS, the DOUT line goes back into three-state.
If the rising edge of CS occurs before 16 SCLKs have elapsed,
the conversion is terminated, the DOUT line goes back into
three-state, and the control register is not updated; otherwise,
DOUT returns to three-state on the 16th SCLK falling edge.
Sixteen serial clock cycles are required to perform the conversion
process and to access data from the AD7298-1.
For the AD7298-1, four channel address bits (ADD3 to ADD0)
that identify which channel the conversion result corresponds
to, precede the 10 bits of data (see Table 8).
When CS goes low, it provides the first address bit to be read in
by the microcontroller or DSP. The remaining data is then clocked
out by subsequent SCLK falling edges, beginning with a second
address bit. Thus, the first falling clock edge on the serial clock
has the first address bit provided for reading and also clocks out
the second address bit. The three remaining address bits and 12
data bits are clocked out by subsequent SCLK falling edges. The
final bit in the data transfer is valid for reading on the 16th falling
edge having been clocked out on the previous (15th) falling edge.
In applications with a slower SCLK, it may be possible to read in
data on each SCLK rising edge depending on the SCLK frequency.
The first rising edge of SCLK after the CS falling edge would
have the first address bit provided, and the 15th rising SCLK
edge would have last data bit provided.
Writing information to the control register takes place on the
first 16 falling edges of SCLK in a data transfer, assuming the
MSB (that is, the WRITE bit) has been set to 1. The 16-bit word
read from the AD7298-1 always contains four channel address
bits that the conversion result corresponds to, followed by the
12-bit conversion result.
CS
DOUT
DIN
t
2
t
3
t
9
t
10
t
4
t
7
t
ACQUISITION
t
8
t
QUIET
t
5
t
6
SCLK
THREE-
STATE
THREE-
STATE
ADD3
WRITE REPEAT CH0 CH1 CH2 CH3 EXT_REF PPD
DONTC
ADD2
12345 13 14
B
15 16
ADD1 ADD0 DB9 DB8 DB0 DON’T
CARE DON’T
CARE
09321-014
Figure 28. Serial Interface Timing Diagram
AD7298-1
Rev. A | Page 21 of 24
LAYOUT AND CONFIGURATION
For optimum performance, carefully consider the power supply
and ground return layout on any PCB where the AD7298-1 is
used. The PCB containing the AD7298-1 should have separate
analog and digital sections, each having its own area of the board.
The AD7298-1 should be located in the analog section on any PCB.
Decouple the power supply to the AD7298-1 to ground with
10 µF and 0.1 µF capacitors. Place the capacitors as physically
close as possible to the device, with the 0.1 µF capacitor ideally
right up against the device. It is important that the 0.1 µF
capacitor has low effective series resistance (ESR) and low
effective series inductance (ESL); common ceramic types of
capacitors are suitable. The 0.1 µF capacitors provide a low
impedance path to ground for high frequencies caused by
transient currents due to internal logic switching. The 10 µF
capacitors are the tantalum bead type.
The power supply line should have as large a trace as possible to
provide a low impedance path and reduce glitch effects on the
supply line. Shield clocks and other components with fast switching
digital signals from other parts of the board by a digital ground.
Avoid crossover of digital and analog signals, if possible. When
traces cross on opposite sides of the board, ensure that they run
at right angles to each other to reduce feedthrough effects on
the board.
The best board layout technique is the microstrip technique where
the component side of the board is dedicated to the ground
plane only, and the signal traces are placed on the solder side;
however, this is not always possible with a 2-layer board.