3 ms·

Burying the lede there! Can someone expand on the bit about how CCDs are like bucket brigade delaylines?

by rwmj 2y ago

equestria 2y ago
It's basically the same thing, except the initial charges in each cell are created through the photoelectric effect when the sensor is exposed to light. After that, it's the same conveyor-belt-style readout proces as for the BBD. It's also why CCDs tended to have problem horizontal or vertical halos around bright lights. Nowadays, most cameras use CMOS sensors, where the amplification and readout circuitry is integrated directly into each photosensitive cell.
Cerium 2y ago
Check out the datasheet for this single row CCD sensor[1]. Look at pages 2 and 6, which show the block diagram and control signal waveforms. There is a single analog output pin. To read the device the "analog shift register" is used, which is a bucket brigade device to move the charge from the photo diode to the output buffer. [1] https://www.spectralproducts.com/pdf/ToshibaTCD1304.pdf https://www.spectralproducts.com/pdf/ToshibaTCD1304.pdf
kazinator 2y ago
A bucket brigade delay obtains a sample of a voltage on one end, and then shifts copy of that charge among the cells to the other end. The delay line as a whole contains a window of samples at any point, but that window is such is not accessed. A CCD line obtains a window of samples directly: the cells are charged according to light sensors. Then this window of samples is shifted out in the same way as a bucket brigade delay line. So the main differences are that the bucket brigade is clocked continuously, running nonstop and that only one of the cells obtains the sample. The CCD runs only briefly after an image has been exposed and capture has been triggered, in order to shift out the samples, and sampling takes place at every cell. A bucket brigade can be slowed down or sped up to change the delay. That affects the sampling rate and therefore frequency resolution. That's how we can create a chorus effect for musical instruments. So the clock speed is a direct functional parameter. Slowing down or speeding up the CCD doesn't make a difference to the result, except that there's likely an ideal range of rates, balancing between the time needed to accurately charge one cell to be equal to its neighbor, while being fast enough to avoid leakage.

Burying the lede there! Can someone expand on the bit about how CCDs are like bucket brigade delaylines?

by rwmj 2y ago

Burying the lede there! Can someone expand on the bit about how CCDs are like bucket brigade delaylines?

It's basically the same thing, except the initial charges in each cell are created through the photoelectric effect when the sensor is exposed to light. After that, it's the same conveyor-belt-style readout proces as for the BBD. It's also why CCDs tended to have problem horizontal or vertical halos around bright lights. Nowadays, most cameras use CMOS sensors, where the amplification and readout circuitry is integrated directly into each photosensitive cell.

Cerium 2y ago

Check out the datasheet for this single row CCD sensor[1]. Look at pages 2 and 6, which show the block diagram and control signal waveforms. There is a single analog output pin. To read the device the "analog shift register" is used, which is a bucket brigade device to move the charge from the photo diode to the output buffer. [1] https://www.spectralproducts.com/pdf/ToshibaTCD1304.pdf https://www.spectralproducts.com/pdf/ToshibaTCD1304.pdf

kazinator 2y ago

A bucket brigade delay obtains a sample of a voltage on one end, and then shifts copy of that charge among the cells to the other end. The delay line as a whole contains a window of samples at any point, but that window is such is not accessed. A CCD line obtains a window of samples directly: the cells are charged according to light sensors. Then this window of samples is shifted out in the same way as a bucket brigade delay line. So the main differences are that the bucket brigade is clocked continuously, running nonstop and that only one of the cells obtains the sample. The CCD runs only briefly after an image has been exposed and capture has been triggered, in order to shift out the samples, and sampling takes place at every cell. A bucket brigade can be slowed down or sped up to change the delay. That affects the sampling rate and therefore frequency resolution. That's how we can create a chorus effect for musical instruments. So the clock speed is a direct functional parameter. Slowing down or speeding up the CCD doesn't make a difference to the result, except that there's likely an ideal range of rates, balancing between the time needed to accurately charge one cell to be equal to its neighbor, while being fast enough to avoid leakage.