Odd stages were switched on one phase, even on the other. However, if all of the switches were on simultaneously then the charge would ripple down the chain not the desired behavior! Instead, the circuit was designed to work in two phases. The switch was activated to transfer the charge from one stage to the next. CCDs were notoriously noisy and had modest signal-to-noise ratios of around 60 dB, comparable to a 10-bit digital system.Įach stage of a CCD was a very simple circuit of a semiconductor switch and one capacitor. When the clock rate was reduced low enough (for long delay times) this "clock leakage" could be audible. The clock used to trigger the S&H-like chain would "leak" into the signal. The BBD uses "sampled analog" and is thus subject to aliasing.ĬCDs also had another characteristic that affected the sound of a bucket brigade delay: clock noise. To change the delay time the sample clock needs to change a slower clock means a longer delay. The number of S&Hs in the CCD is fixed so the delay time through the CCD is constant for a given sample clock frequency. This is analogous to the old way water was brought to fires, the bucket brigade hence the name. So samples where passed from one S&H to the next at a rate determined by the clock. When a sample trigger occurred one S&H captured the voltage held by the previous S&H. The S&H triggers were all clocked by the same signal think of it as a sample clock. One way to think about CCDs is that they were a very long string of analog sample and holds (S&H). BBDs made use of a then new semiconductor device, the CCD (charge coupled device). If your goal is to emulate the behavior and sound of a bucket brigade delay (BBD) then some background on how BBDs worked may be helpful.
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