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an analog to digital converter problem

Discussion in 'Electronic Design' started by Power boy, Sep 17, 2012.

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  1. Power boy

    Power boy Guest

    I have a linear ccd signal input, the ccd analog output shift out
    pixel's voltage at max frequency of 1MHz. According Nyquist the raw
    signal's bw is 500kHz.
    check page 6 in below:

    I need to build an afe + adc circuits.

    I want to increase the dynamic range. The spec says noise is 2mV. Who
    knows the measurement bandwidth? whatever, just say, 2mV.

    I picked an adc, super good, with bw of 16MHz. I want to do an AC
    coupled, bandpass afe. I calculated the variable gain should be 0-60dB
    or less. I want to limit my afe's bw, or limited harmonic for the ccd
    analog inputs. Remove the inband white noise as much as possible. but
    I want to consider the in band ripple will generate the uncertainty. I
    want to control the in band analog uncertainty within 0.1%. How many
    harmonics should I choose? To do a reverse Fourier transform might
    sovle this problem but I am far from the textbooks.

    I guess I need 500kHz * 15th = 8MHz. how about the ripple introduced
    by the 1st to 15th harmonics for square wave?
  2. Power boy

    Power boy Guest

    thanks but you still didn't point out the bandwidth even this is
    spatial. if this is spatial, I treated as sqare wave impulse, the bw
    for this is still 1/(2*delta_T). To sample this ccd with big dc
    offset, pink noise and white noise I want to remove the noise , dc
    offset. However, a HPF introduces too much distortion due to the in
    band phase delay. I can only use an AC coupled lpf. the pink noise is
    still there. I couldn't just directly send it to adc which includes
    too much noise. the white noise's spectrum density is flat that's why
    I narrow the input bandwidth. I tested a little bit if I use ac
    coupled, bessel or butterworth with cutoff at 16MHz it just introduced
    rising edge delay. if I use HPF the signal is totally distorted,
    within 1us the voltage level is tilting due to the phase delay. I know
    the pink noise is still there.

    my signal is about 5 uv with the dc offset 3V. noise is about 2mV. I
    want to do 100 times averaging which improve 10 times snr. and I will
    do other kind of filtering after digitized the signal.
  3. power boy

    power boy Guest

    I just changed detector and design approach after research a few days.

    My current solution will be dual slope integration plus correlated double sampling technique. I figured out the noise source (readout, photon, dark) and some methods to remove them.
    thank you all.
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