ADA2200 Question

Question

Dear Sir/Madam,

I 
 use 
 ADA2200 
 for 
 
 testing 
 
 in 
 
 a 
 
 project 
 , 
 and 
 need 
 to 
 measure 
 
 the 
 
 sensor 
 
 input 
 
 signal 
 's 
 
 amplitude 
 
 and 
 
 phase 
 .

1 
 . B 
 ecause 
 input singla 
 could not 
 
 guarantee 
 
 constant 
 
 within 
 a 
 short 
 
 time 
 , 
 
 I 
 
 want to 
 
 use 
 
 2 
 
 ADA2200 
 to 
 
 realize above function 
 , 
 one 
 is for 
 
 phase 
 
 detection 
 , 
 
 another 
 
 piece 
 is for 
 orthogonal 
 
 detection, 
 I 
 do not 
 
 know 
 
 whether it is avail 
 able 
 ?

2 
 . Because it is best to use sine excitation for the 
 sensor 
 
 excitation 
 , 
 
 RCLK 
 goes through 
 3-order

active 
 
 low 
 - 
 pass 
 
 filter 
 
 into 
 
 sinusoidal 
 
 ( 
 frequencies 
 
 4KHz 
 ) 
 , 
 is 
 this 
 
 solution available 
 ?

Thanks.

ADIApproved · Accepted Answer

Yes, using 2 ADA2200 would allow you to measure both amplitude and phase of the signal simultaneously. The idea is to run both ADA2200s in parallel with a shared clock. You would run one in the default configuration, one with a 90 degree phase offset. This would give you an in-phase and quadrature measurement. From these 2 measurements, the phase and amplitude can be calculated as discussed on page 16 and 17 of the datasheet. 
 Yes, applying a filter to RCLK to generate the excitation signal is a good approach as you are ensured the frequencies are locked. You do want to make sure amplitude and phase drift is minimized in your filter as the drift will be indistinguishable from a phase change in your measurement. This means using a Bessel or Butterworth filter is a better choice than a Chebyshev filter.)

libin265@163.com · Answer

Dear brianharrington , 
 I am a Chinese engineer, please forgive me for my bad English. I am currently developing luminescent dissolved oxygen (LDO), which is achieved by detecting the phase shift between fluorescence and excitation light, the phase shift Is related to the concentration of dissolved oxygen. 
 
 As the phase shift is small, the dissolved oxygen concentration changes from 0% to 100% when the phase shift is only about 10 °@10KHz, so in order to ensure a certain degree of accuracy I use the relevant detection method, using a single spectral excitation sine wave excitation blue LED light source, and then photocell Receiving fluorescence emitted by fluorescent materials, through the AD8615 I / V conversion, and then by the BPF after the relevant part of the input test for the relevant detection.

As the ADA2200 phase detection accuracy is 0.0093 °, I would like to use ADA2200.However, RCLK of ADA2200 is square wave instead of sinusoidal. If RCLK is used to modulate LED, then the signal received by photoelectric tube after I / V conversion of AD8615, AD8615 output signal should be the same frequency as RCLK, Contains the fundamental frequency, also contains odd times the fundamental frequency of the harmonics, so that the ADA2200 phase-locked output signal after the conversion to phase there will be errors, right?

One thing I can not confirm, this AD8615 output signal through the ADA2200 IIR filter will become the same frequency with the RLCK sinusoidal signal, if so then ADA2200 in my system to detect the accuracy of the phase can be accurate.

The problem is bothering me, and I very much hope that you will give me some advice!

China's New Year has just passed, 
 I hope you can share the joy of our holiday! Blessing of the Chinese New Year!

Wishing you prosperity!

libin265@163.com · Answer

Dear brianharrington , 
 Thank you very much for your answer!Sorry,I have a few questions to ask. 1. I understand the square wave reference demodulation of the same frequency square wave signal when the odd harmonic to bring the noise increase is 1dB, and convert the ADA2200 output using an ADC with a synchronous sampling clock, using the ADC's digital filter to suppress Harmonic noise. So in order to better reduce the demodulation back to the DC odd harmonics, I ADA2200 before adding an 8th-order, lowpass filter (such as MAX297), this can? 
 2. 2 ADA2200 in the same phase and quadrature measurement need to share the same clock, and ADA2200 reset, device is configured to generate a clock if a crystal or resonator is placed between the XOUT and CLKIN pins, then the ADA2200 can directly receive the external clock Do not have to set the register 0X0028 bit1 bit is 1? Otherwise, through the SPI configuration can not guarantee two ADA2200 difference of 90 °. 3. If the ADC with a synchronous sampling clock is used to suppress the even harmonic spurs of the PSD output, then the quadrature phase-locked output of the two ADA2200s also requires two simultaneous clock ADCs(such as 2 AD7192),right? 
 4. I used to do with the AD5933 organic micro-conductivity measurement, AD5933 although is used to measure the impedance, but it is a sinusoidal output excitation, and its signal processing is DFT, and finally through the results of the excitation frequency of the complex impedance Data, which have phase information, I think that if the AD5933 output sinusoidal signal to modulate the LED light source, then the I / V conversion, and then input to the AD5933 by BPF, then AD5933 will DFT, the final output of the corresponding complex Impedance data, through the complex impedance data can be calculated phase information, This is easier to handle than the ADA220 case, I do not know this method to detect the phase is appropriate?

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