How to enable high-accuracy CW Doppler through discrete, precision data converters

RE: How to enable high-accuracy CW Doppler through discrete, precision data converters

Kuba Sunderland-Ober — Fri, 06 Oct 2023 00:39:15 GMT

It’s worth saying that Doppler measurements are amplitude-insensitive. The output signal is a frequency difference. The reference source for the ADC can be pretty lousy as long as it has low noise in the ADC bandwidth of interest. And even then, the contribution would be mainly to the SN ratio, not accuracy overall. In contrast with, say a DC absolute measurement, where reference voltage errors show up in the output.

RE: How to enable high-accuracy CW Doppler through discrete, precision data converters

Evan Sawyer — Wed, 12 Apr 2017 17:16:26 GMT

Hi Eric,

Great questions!

Regarding the use of two discrete ADCs instead of a simultaneously sampled two channel device, it comes down to maximizing signal chain accuracy. A 20 bit device (ADS8900B) was chosen to maximize resolution without digital filtering (which adds delays). From there, the device performance became the next critical factor (see page 6 and 7 of the datasheet for the min/max INL, SNR, THD, SINAD, etc.)

Regarding the generation of the quadrature inputs, the generation is up to you based on your system performance requirements and key cares (size, power consumption, performance, etc.).

RE: How to enable high-accuracy CW Doppler through discrete, precision data converters

Eric Fletcher — Mon, 10 Apr 2017 15:12:45 GMT

* Instead of using two separate SAR-ADC's, why not have dual matched ADC's like the Analog Devices AD7903 ( 16 bits- 1MSpS), the Linear Technology LTC 2321-16 ( 16 bits-2MSpS ) & the Maxim Integrated MAX 11960 ( 20 bits-1MSpS ) ?

* For the input conditioning and generation of quadrature inputs, why not mount a Programmable Hilbert Transformer

with bands shiftable from 400 kHz-400 Hz to 100 Hz-0.1 Hz ?