Electronics > Beginners
Analog Delay
David Hess:
--- Quote from: Yansi on May 06, 2019, 07:39:14 am ---
--- Quote ---Mechanical transmission lines using springs with transducers at each end also work as audio delay lines.
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???
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I mean the mechanical transmission line is literally a spring. A spring is the mechanical equivalent of a transmission line loaded with a high dielectric constant for a very low velocity factor.
They were commonly used for audio reverberation effects.
Yansi:
But I have already mentioned spring reverbs. Why I was quoted in #9 then?
richard.cs:
--- Quote from: TimFox on May 06, 2019, 01:11:20 pm ---With respect to analog delay lines: I remember a feature in Electronic Design, sometime around 1990?, where Plessey had made a fast-sampling bucket-brigade device to allow rapid signal capture before feeding the samples into a slower ADC for DSO application. The bucket-brigade was quite long, and didn't fit into a roughly square form factor on the chip, so it was spread out as a Z shape, with wasted space inside the Z. The designer had inserted a small steam locomotive shape (from his kid's coloring book) into the gap, since the line looked much like rails separated by ties (sleepers). Tektronix was famous for illuminating their schematics, but this is the only such artistic effect of which I am aware in a monolithic device.
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I remember hearing about that when I was working at a former Plessy site, several owners later but with many of the original staff. Apparently it came up in a court case where someone had copied the masks but claimed that the design was obvious and they'd come up with it independently.
Gyro:
Just looking on ZeptoBars. They have recently posted die shots of the MN3102 Bucket Brigade clock driver chip and the MN3207 1024 stage Bucket Brigade analogue delay line. Nice photos...
https://zeptobars.com/en/
Bassman59:
--- Quote from: IvoS on May 05, 2019, 01:07:30 pm ---
Just a general question on how is the analog delay topology executed. I have an idea of how the signal in digital domain can travel, something like: ADC-processor-memory-DAC or something like that. But how they really do it in analog delays for a musical instrument for example.
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The Bucket-Brigade Device was the most common way to get specific delay times for audio use. They work in much the same way as the Charge-Coupled Device (CCD) works for imaging, except instead of the input to the delay being a pixel voltage, it's a signal voltage fed in.
The BBD is an apt name because that's basically how it works. You have a string of charge "buckets" all in series. The input signal is "clocked" into the first bucket, and then on each clock, all of the charges in each of the buckets is transferred to the next bucket in the string. At the end of the line, the output of the last bucket is low-pass filtered and buffered to drive the delay line output. It is sampling, since on a regular basis a snapshot of the input signal is captured and dumped into that first bucket. But it is not quantization, as the signal in the buckets is never converted to a digital number. It remains just a voltage (a charge on a capacitor) through the entire delay line.
Delay time is set by two mechanisms, which are used together. One is simply the number of "buckets" in the string. More buckets, more delay. The second is the clock rate. Faster clocking means shorter delay time. The clock rate is the sample rate, so the lower the clock rate, the lower the bandwidth of the system. The upper limit to clock frequency is set by the clock drivers. Each bucket is connected to the previous and the next by FET switches, and the clock controls the gate of each, they're all connected in parallel. Thus the clock has to be able to drive the capacitance of hundreds of gates in parallel.
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