Maxim Integrated MAX2769 GPS Receiver - Manual (Page 6)

the input level to -65dBm. It should remain approximately the same (indicating AGC is working).
LNA2 Tests
12. Switch to LNA2 (CONF1<14:13> = 01). Input a -60dBm, 1575.42MHz CW signal at J6. Measure LNA2 gain at
J8 and record. Raise the input level until you get 1dB compression (P1dB). This is a repeat of steps 4 and 5 with
LNA2. (Note again that the cascaded P1dB is determined by the mixer stage.) Cascaded gain is the linear gain
measured here plus the gain from the mixer-in port to J2 from step 7.
13. If an NF meter is available, measure the LNA2 NF between J6 and J8. Then measure the NF following the
procedure in step 9. Be sure that the AGC control is turned off so you can control the output level,
CONF2<12:11> = 10.
14. With default settings, measure IP3 using LNA2. Combine two sources of -55dBm input at F1 = 1587.42MHz
and F2 = 1599.42MHz (where 2 × F1 - F2 falls in-band at 1575.42MHz) and inject into J6. Measure the strength
of the 4.092MHz product at J2 (Q out)—analog mode must be selected. Drop both inputs by 1dB and note that
the product drops by 3dB. (If not, you are compressing the signal and need to use a lower input level.) Calculate
IIP3 as in step 8.
Digital Tests
Digital measurements should be made at J9 A, B, C, and D. It has been discovered that the 74LV07 driver chip (U28) originally
designed onto the board does not properly buffer these signals to allow them to be passed back to the computer on connector
JDR1. To use these output signals to drive other circuitry off board, they may need to first be separately buffered.
15. Change to a digital output (CONF2<5:4> = 00) so that CONF2 = 855028C, and monitor the signal on an
oscilloscope. You should have a square-wave CMOS output (2.8V amplitude) at J9. With CONF2<27> = 1, both I
and Q signals should be present.
Appendix: Suggested Register Settings for Initial Test
CONF1: Test: A2959A3
This register:
Enables the chip (default)
Disables the idle (default)
Sets default current programming
Sets non-default LO current programming
Sets default mixer current programming
Selects 13MHz passive filter pole at mixer output (default)
Selects LNA1 active (default; equivalent to grated mode when there is no current load on the ANT BIAS pin)
Enables mixer (default)
Turns off bias to external active antenna (default is bias on)
Selects F
C
= 4.092MHz
Selects 2.5MHz polyphase IF bandpass filter
Selects 26dB IF filter gain (default is 17dB)
CONF2: Test: 85502AC
This register:
Selects both I and Q channels (default is I only)
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