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Entry  Tue Apr 26 17:06:37 2011, Mingyuan, Tara, DailyProgress, Creak, start crackling 
    Reply  Thu Apr 28 21:55:25 2011, tara, DailyProgress, Creak, start crackling chopping.pdf
       Reply  Fri Apr 29 18:39:37 2011, tara, DailyProgress, Creak, start crackling 
          Reply  Wed May 11 22:17:35 2011, tara, DailyProgress, Creak, start crackling 1khz.pngf_t_response.png
       Reply  Fri Apr 29 21:23:15 2011, tara, DailyProgress, Creak, start crackling ad734_crackle.pdf
          Reply  Thu May 12 23:18:27 2011, ryan, tara, DailyProgress, Creak, start crackling ad734.png
Message ID: 190     Entry time: Thu Apr 28 21:55:25 2011     In reply to: 189     Reply to this: 191   192
Author: tara 
Type: DailyProgress 
Category: Creak 
Subject: start crackling 

 

 I ordered 5 of AD734 and thinking about how to make a circuit for squaring the signal.

 

    The "chopping" signal readout technique requires that we square the signals.  Basically we need to (as rana suggested):

(1) square the signal from PD, (after 10-100Hz bandpass) to convert it to power, and band pass it again.

(2) square the driving signal (might be varied from 0.1- 1Hz.) This is illustrated in the diagram as doubling the frequency ("2 x freq" box.)  The driving signal for PZT is offset. So the signal is  V drive = A + B xsin (2pi fdrive t) with A > B. This ensures that the voltage on one end of the PZT is always higher than another end. We might need to high pass this signal first, to get a signal with only 2 fdrive frequency after we square it.      

(3) multiply signal from (1) and (2) to demodulate the signal.

 

Basically, 3 multipliers are needed.

The first one is for (1), so the input frequency is ~ 10 -100Hz, and the output is 20-200 Hz.

The second multiplier is for (2), the signal is ~ 0.1 - 1 Hz, but this one might have large DC term after we square it.

The third one is for (3), this one has to multiply 2 low f signals together which is quite similar to (2), so the design can be the same.

 

I'll consult Frank and/or Koji again before finalize the multiplier circuit.

 chopping.pdf

 

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