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I am new to FMCW radar and I am using a TI module. I have been reading the TI reference material and they keep mentioning the parameter "ADC Sampling Rate". I am confused by what this means in terms of number of ADC samples, chirp length, sampling rate, and other chirp parameters. This picture shows the sensor configuration in TI's mmWave Studio. Based on how this is setup how would I determine the ADC sampling rate?

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  • $\begingroup$ Ummm, no picture $\endgroup$
    – David
    Jul 28, 2022 at 17:45

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Without the picture we can't address some specifics that you might be looking for, but in general:

FMCW radars find range by generating beat frequencies. After the beat frequencies are generated, it is these signals (linearly combined sinusoids) that you are digitizing via the ADC. You perform the DFT on the collected data, and can map the frequencies to ranges.

Having said that, the range window you want to observe is dependent on the range of frequencies you're willing the capture. If you want a wider range window, you need to sample at a higher rate in order to do so. This is the main relationship to consider in a FMCW system when it comes to the ADC.

When it comes to the pulse width $\tau$, or chirp length, the number of samples $N$ will increase as the chirp gets wider or if the sampling rate $f_s$ increases:

$$N = f_s\tau$$

The bandwidth $\beta$ of the chirp establishes the range resolution of the system in addition (along with the pulse width) to the slope of beat frequencies $f_b$ generated:

$$f_b = \frac{2R\beta}{c\tau}$$

For a given maximum range, increasing the bandwidth also increases the maxium beat frequency generated, and thus the ADC must be able to sample it.

Note that these beat frequencies are usually an order of magnitude smaller than the bandwidth $\beta $ of the chirp, enabling the use of a slower sample rate and cheaper ADC. This is one of the main benefits of FMCW over traditional (correlation-based) radar systems.

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Actually there is a relationship between ADC sampling frequency and max intermediate frequency value. These are directly proportional and this parameter directly proportional to maximum range value. The higher these values, the greater the maximum distance you can detect.

For other parameters, follow This reference

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