Gain, Frequency Response and OIP3 Measurements:
1) Connect test equipment and power supply to the demo board as shown in Figure 3.
2) Set ENA and ENB to Logic HIGH state (Refer to Table 1 and Table 2). The IC is in Standard
Operation Mode (both amps are ON) and the amplifier has maximum gain.
3) Perform single CW tone frequency sweep (100 KHz to 600 MHz) and measure gain and
frequency response. NOTE: For a demo board with a type “A” output (with 50 ohm pull-up
resistors) external 180o combiner should be used. Measurements can be also done using one
output. In this case the other output should be terminated externally. One-output measurements
have no common mode rejection and will show higher output noise.
4) Apply two input CW tones and perform two-tone output IM3 product measurements at different
output power levels from 0 dBm to +10 dBm (per each tone).
NOTE: For a demo board with a type “A” output (with 50 ohm pull-up resistors) an external
180o combiner should be used. Single output measurements will show an elevated noise floor.
For single output measurements, the second output should be terminated externally with 50 ohm
load.
Notes for Two Tone Measurements:
1. High quality signal generators (with low level of output harmonics and reverse power
protection) should be used. Low pass filters should be employed at the signal generator outputs
to minimize higher order harmonics to –90 dBc or better. Attenuator pads at the signal generator
outputs will also help to minimize reverse power problems.
2. A high sensitivity/high dynamic range spectrum analyzer should be used. Care must be taken to
operate the spectrum analyzer in linear mode to avoid additional IM distortion products
produced by the instrument itself. It is advisable to use a narrow bandpass filter at the spectrum
analyzer input to select IM products and attenuate main tones. In this case, a 10 to 20 dB
attenuator should be placed between the LT5514 output and the BPF input to provide broadband
matching.
Additional application notes (refer to the complete demo circuit schematic):
• In a type “B” output (demo circuit with output RF transformer), resistor R7 is 255 ohm. This
provides the best output return loss. For best IM performance this resistor should be removed.
This will result in a 5dB IM3 performance improvement.
• R19 is a zero ohm jumper. R19 can be removed if differential output is desired.
• Output transformer T2 can be removed and pull-up resistors (50 ohm) can be placed at R20 and
R21 locations at the topside of the demo board. Also, pull-up inductors (820 nH) can be placed
at R20 and R21 locations as well. This will result in higher output impedance. For proper
impedance matching 50 ohm resistors can be connected in parallel with pull-up inductors.
Coupling capacitors (not shown on the demo board schematic) can be placed instead of the
output transformer T2, connecting output pins 15 and 16 to the output SMA connectors J2 and
J4.
DC550A Demo Board
Quick Start Guide 8