Evaluation of ADC Selection for GPS Signal Processing with Interference Management

Question

If the received power of an antenna is at -95dBm (-125dBm gps signal + 30dB interference) and the thermal noise with 25MHz signal BW is -175dBm/Hz + 73dBm = -102dBm. Given the information, how can i choose an appropriate ADC?

Right now i am considering ad9257s-csl, based on:

The full scale input power is 2V at 200ohms = 4dBm. A gain of 70dB will put the gps signal, thermal noise and the interference at -55dBm, -32dBm and -25dBm respectively. This gives gps signal to quantization noise ratio of about 10dB.

Assuming i can suppress the interference during the processing stage and de-spread the gps signal to get a process gain of 53dB (10MHz/50Hz), this will give me about -55dBm + 50dB +32dBm= 27dB SNR?

Now is this process correct?

(Not quite sure about how processing gain works, take it with a grain of salt.)

Answer 1

If the received power of an antenna is at -95dBm (-125dBm gps signal + 30dB interference) and the thermal noise with 25MHz signal BW is -175dBm/Hz + 73dBm = -102dBm. Given the information, how can i choose an appropriate ADC?

signal-to-noise ratio (SNR): $\text{SNR} = -95 \, \text{dBm} - (-102 \, \text{dBm}) = 7 \, \text{dB}$. It means that ADC needs a minimum dynamic range of 7 dB to distinguish the signal from the noise. But, given practical considerations and potential interference, it would be wise to use an ADC with at least 8–10 bits, providing a dynamic range of 48–60 dB. This extra margin will handle fluctuations and ensure reliable signal detection without clipping.

In addition, for a 25 MHz bandwidth, according to the Nyquist rate theorem, the minimum sampling rate should be twice the signal bandwidth, i.e., 50 MSPS. But, in practice, it’s beneficial to oversample slightly, so an ADC with a sampling rate of 60-100 MSPS would be more robust for this application.