# an analog to digital converter problem

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

1. ### Power boyGuest

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:
http://www.zygo.btinternet.co.uk/tcd1304ap.pdf

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 boyGuest

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 boyGuest

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.