Bucket Brigade Devices (BBDs)

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Published On:

Nov 4, 2024

Last Updated:

Dec 9, 2024

Bucket brigade devices (BBDs, a.k.a. bucket brigades) are analogue delay ICs that “shunt” charge along a series of switched capacitors to create a delay. Moving charge from one capacitor to the next is not a simple process (if you connect two capacitors together in parallel, only some of the charge is transferred until the voltages are equal). Bucket brigades use a clever technique to completely transfer the signal (represented as charge) from one capacitor to the next. They do this representing the signal as an absence of charge, and a clever circuit which involves transistors and capacitors with one of their plates connected to the gate. This is a placeholder for the reference: fig-bucket-brigade-delay-basic-internal-schematic shows a basic internal schematic of a bucket brigade device.

A basic internal schematic of a bucket brigade device¹.

This is a placeholder for the reference: fig-bucket-brigade-delay-basic-internal-schematic was the initial design, but is suffered from a few problems, the most serious being poor transfer efficiency².

Bucket brigades are analogue in amplitude, but discrete (digital) in time. Thus they suffer from the same aliasing issues all other digital sampling methods do. Care must be taken to ensure the input signal has no frequencies above half the sampling rate to avoid aliasing. This is typically done with an analogue low-pass “anti-aliasing” filter. Second-order Sallen-Key filters are a common choice due to their effectiveness and simplicity.

History

The bucket brigade in it’s integrated form was first invented by F.L.J. Sangster at Phillips in 1968² ³.

Bucket Brigade Devices (BBDs)

History

Further Reading

Footnotes