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Is it possible to use the ADA2200 without SPI configuration?

Question asked by ppapuli on May 11, 2017
Latest reply on Jun 28, 2017 by iamPhil



My group members and I are using your synchronous demodulator in our senior design project. Our goal is to measure the light absorbance of blue light in algae.


To do this, we shine blue (absorbed), and green (not absorbed) light into a photodetector, which we then amplify to create a complex square wave with two mixed signals. Then, we use two of your chips (ADA2200) to separate the signals into their original waves and measure the DC offset to give an idea of how much algae is present in the water.


When trying to set up the device as a lock-in amplifier, we were under the impression that we didn't require any previous configurations or register initialization, however, the more we test the device the less we can identify any problems with what we're doing.


We're testing the chip as a standalone outside of our circuit to try and recreate the results.This is the configuration we're currently testing to try to separate the 300Hz signal from a complex sine wave we created using two signal generators:


Clkin = 19.2kHz
Synco = Floating
CS/AO = Vdd = 3.3V
INP = Mixed signal of 300Hz+500Hz
INN = VOCM ==> bypassed to ground through a capacitor
RCLK ==> INP (should be 300Hz)
OUTP = our output
RST = VDD through a LPF


Our goal is to use the chip without initializing the SPI interface. However, if this isn't possible, we would like to know how to initialize it, or what we're doing wrong with our configuration.
To our understanding RCLK should be 64x lower than our master clock of 19.2kHz...
19.2k/64 = 300Hz.


In order to verify if it's working, we raise the amplitude of the 300Hz signal and measure the DC output voltage to see a rise that is proportional to the amplitude. However, the DC output voltage does not raise with an increase in amplitude.


Can you please provide us with a default set up for what we're trying to produce, we've come to a standstill for a few days and can't get any meaningful results.


I've tried to be as detailed as I can, but feel free to ask any follow up questions if something is unclear.