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APPLICATION NOTE
BGA2022, RX mixer 880, 1950 and 2450 MHz
Abstract This report describes three demo boards on which the BGA2022 has been
applied as a down-mixer:
Conversion Gain OIP3 NF
880 to 80 MHz 5 dB 4 dBm 9 dB
1950 to 80 MHz 5 dB 7 dBm 9 dB
2450 to 280 MHz 6 dB 10 dBm 9 dB
The report will briefly deal with considerations about designing the RF port matching network,
the LO port coupling and the IF port matching network. Then the diagram of the circuit and the
PCB will be given. Tables with components and achievements complete the report.
This document has been based on four separate reports by Onno Kuijken:
Application note: BGA2022 RX mixer for 880 MHz low noise : RNR-45-99-B-0222
Application note: BGA2022 RX mixer for 1950 MHz : RNR-45-99-B-0226
Application note: BGA2022 RX mixer for 2450 MHz : RNR-45-99-B-0255
Keywords: BGA2022, Mixer, RF, Conversion Gain, IP3, NF
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Introduction
The BGA2022 is a low-power, low-voltage silicon MMIC mixer that has been designed for high
gain and linearity. It is primarily intended to be used in the receive chain of GSM, TDMA and
CDMA portable ‘phones. Because the performance is largely determined by external
components, the device is extremely flexible in use. It can be used for frequencies up to about
2.5 GHz. In the application examples, RF signals of 880, 1950 and 2450 MHz will be converted
to IF frequencies of 80 or 280 MHz.
Description of the electrical circuit
The electrical diagram of the circuit of each board has been depicted in figure 1. For flexibility
reasons, the peripheral components shown are “generic” components. They are not
necessarily all present. A list of components on this application PCB and their values is given
in table A.
RF input circuit
The input has been matched to 50 Ω by the three-element network C1, C2 and L1. C1 and C2
serve as a DC block of the RF input port of the BGA2022. Finally, C2 is vitally important for
(3) Vss
(4) IF
(2) LO
(5) RFfb
(6) RF
C1
L1
C2
C7 C8
R2
R4 C4 C3
C5
L2 R1
L3 C6
BGA2022
(1) LOgnd
Figure 1 Electrical circuit diagram
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suppression of direct breakthrough and hence for noise performance. Its value should be
chosen such that it is series-resonant with L1 at the IF frequency.
Intermodulation can be improved at the cost of Conversion Gain by placing an additional
inductor between RF-feedback pin and ground. On the PCB, there is no place reserved for
this additional inductor.
LO input circuit
The capacitors C3 and C4 supply the LO
signal to the circuit. For optimum
performance, they should be series-
resonant with the inductance of the
leadframe, which is about 0.9 nH per lead.
The LO input is internally matched to
50 Ω, see figure 2. For optimum noise
performance, attention should be paid to
the spectral purity of the oscillator. In case
sufficient spectral purity, especially at
offsets of an integer multiple of the IF
frequency from the carrier cannot be
guaranteed, a band pass filter should be
inserted between the local oscillator and
the LO input pin.
On PCB, a footprint for a filter has not
been been designed.
IF output circuit
The Conversion Gain mainly is fixed by the
output load resistor R1. This resistor can
be chosen up to a limit of about 3 kΩ. As
R1 becomes higher, the match to 50 Ω
will be more complicated; bandwidth of the
matching will be narrower, high Q
components will be required.
The matching itself is performed through
L2, C6 and L3. In case a relatively high-
impedance load is used, such as a SAW filter, the matching between the mixer output and this
load becomes easier.
L1 L2 L3
BGA2022
M9811_{12,13}
(MPW2022_[12])
Vcc
LO
RF
IF
C3
C4
C1
C2 C5
C7
C8
C6
R4 R1
R2
Figure 3 Layout of the application PCB
RF-feedback (5)
LO (2)
IF (4)LO - GND (1)
RF - signal (6)
Bias
control
50 Ω
LO-termination
figure 2, internal diagram BGA2022
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L2 and C5 form a band pass filter for the IF frequency. This filter provides IP3 improvement.
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Description of the PCB layout
As in any RF application, the PCB layout is vitally important for a good performance. The
layout of this application PCB is shown in figure 3.
The input matching circuit should be as close to the MMIC as possible, and especially in the
parallel branch to ground (C2 and L2) there should be as little as possible extra inductance.
The loop formed by the LO input trace, the LO coupling capacitors C3 and C4 and the
grounding via should be as small as possible in order to reduce LO radiation and susceptibility
to radiated interference.
The supply should be well decoupled close to the MMIC, not only with a large-valued capacitor
C7, but also with a smaller RF decoupling capacitor C8. For optimum noise and
intermodulation performance, this RF decoupling capacitor should be self-resonant at the LO
frequency.
880 MHz 1900 MHz 2450 MHz Component
R1 1k2 2k2 3k3 Philips 0603 (blue)
R2 22 22 18 Philips 0603 (blue)
C1 12 pF 1.5 pF 1.0 pF Philips microwave 0603 NPO
C2 390 pF 1.5 nF 82 pF Philips 0603 X7R (1.5 nF 330
pF, 390 pF), Philips microwave
0603 NPO
C3 39 pF 6.8 pF 2.7 pF Philips microwave 0603 NPO
C4 39 pF 6.8 pF 2.7 pF Philips microwave 0603 NPO
C5 27 pF 15 pF 2.2 pF Philips microwave 0603 NPO
C6 100 pF 10 pF 100 pF Philips 0603 NPO
C7 22 nF 22 nF 22 nF Philips 0603 X7R
C8 56 pF 10 pF 6.8 pF Philips microwave 0603 NPO
L1 10 nH 2.7 nH 1.8 nH TDK MLG1608
L2 220 nH 150 nH 220 nH Coilcraft 0805CS
L3 470 nH -- 120 nH Coilcraft 1008CS
Table A, list of components
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Achievements
The measured performance has been summarised in table B.
Conditions: Vsupply=2.8 V, Isupply=6 mA T=25 oC
880 MHz 1950 MHz 2450 MHz unit remarks
Conversion Gain 4.7 5.0 6.2 dB RF power is –30 dBm
LO power is 0 dBm
Noise Figure 9 9 9 dB DSB, notch filter at LO port
OIP3 4 7 10 dBm RF power is –30 dBm
LO power is 0 dBm
P1dB -9 -6 -7 dBm LO power is 0 dBm
ÃRF <10 <10 <10 dB RF power is –30 dBm
ÃIF <10 <10 <10 dB
ÃLO <10 <10 <10 dB LO power is 0 dBm
RF to LO -50 -16 -15 dB No LO signal, PRF=-30 dBm
LO to IF -64 -19 -45 dB No RF signal, PLO=0dBm
RF to IF -70 -11 -38 dB Without conversion, no LO signal
PRF=-30 dBm
LO to RF -41 -32 -35 dB No RF signal, PLO=0dBm
Table B, measured results of demo boards
Remarks:
- At 3 V supply, Conversion Gain and IP3 figures slightly improve.
- Noise figure measured with HP8970A without additional mixer test setup, standard
measurement mode.
