Maxim Integrated MAX2769 GPS Receiver - Manual (Page 5)

TEST1: 1E0F401
TEST2: 14C0002
Make sure SHDN and IDLE are set to 1, the disabled state for both.
3. Measure +3V current consumption at W19 and W20.
4. Input a -60dBm, 1575.42MHz CW signal at J7. Measure the signal at J8 and record the LNA1 gain. Take into
account the loss on the board traces at 1575MHz around 0.35dB.
5. Raise the input level until you get 1dB of compression (P1dB). (This is not a specified parameter, but you
should get a number around +8dBm.) Be sure to gain correct any line losses.
6. Connect a short, low-loss cable from J8 to J12 to connect the LNA1 output to the mixer. Decrease the input to
-110dBm and measure the system gain by monitoring the 4.092MHz output at J2. It should be around 110dB,
resulting in a 0dBm output.
7. Set the maximum GAININ level by setting <3:27-22> to 63 (CONF2: 85512AC and CONF3: FEFF1DC).
Decrease the input to -115dBm and measure the gain—it should be around 115dB. The input level should be
adjustable through changes in GAININ. Decrease GAININ to the minimum by setting CONF3: 02FF1DC and once
again measure the gain. It should be around 55dB.
8. Measure IP3 using LNA1. Combine two input sources (perhaps around -55dBm input), at F1 = 1587.42MHz
and F2 = 1599.42MHz (where 2 × F1 - F2 falls in-band at 1575.42MHz) and inject into J7. Measure the strength
of the 4.092MHz product at J2 (Q out). Drop both inputs by 1dB, and note that the product drops by 3dB. (If not,
you are compressing and need to use a lower input level.) OIP3 = (3 × P
OUT - product)/2, so
IIP3 = (3 × P OUT - product)/2 - gain. This reduces to (3 × (P IN + gain) - product)/2 - gain =
(3 × P OUT - product + gain)/2. With a minimum (55dB) gain, P OUT = 5dBm. A typical 3rd-order product seen on
the output spectrum at minimum gain might be -5dBm, in which case IIP3 = (3 × (-55) + 5 + 110)/2 = -25dBm.
9. Measure the LNA1 NF with an NF meter. The NF of the mixer stage can be measured using the gain method:
by setting gain to max (see step 8), reducing the spectrum analyzer resolution bandwidth, and measuring the
output S/N ratio. You need to have measured the exact system gain. For example, the input noise is -
174dBm/Hz. Using an input of -100dBm and assuming around 90dB gain for the mixer stage, the receiver will
not be in compression. The input S/N in a 1Hz bandwidth would be -74dB (S = 100dB/Hz, N = 174dBm/Hz). We
might measure an output noise floor at J2 of -73dBm/Hz, yielding (with a -10dBm output) an SNR around 63dB.
The NF of the system would then be the degradation in the S/N ratio, or 11dB. The result is approximate
because measurement precision is poor. However, as the result is large and precision for this value is not critical,
this approximate result is sufficient. Once again, subtract the input losses on the board (roughly 0.35dB) from all
measured results. Knowing the gain of LNA1, you can then calculate cascaded NF.
You could use the gain method or the y-factor method to measure the NF for the entire cascaded chain, but this
result would once again be approximate.
10. Return to the test register settings from step 2 and use an input level at J12 that is at least 10dB below the
value that leads to 1dB compression, typically -110dB. Sweep the input frequency from 1572.9MHz to
1577.9MHz to yield a passband of 2.6MHz for the IF bandpass filter. This measurement can be made by using
the maximum hold option on the spectrum analyzer.
11. Set up the AGC in the autonomous mode (AGC on with independent I and Q), where CONF2<12:11> = 00.
Feed a signal into the LNA1 input at -150dBm and select LNA1. Note the tone power at the output while raising
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