Design example

High-Voltage Sample-and-Hold Amplifier Circuits

These analog circuits combine sample-and-hold with high-voltage amplification. A sample-and-hold circuit captures an analog voltage and retains it between updates; the retained value gradually drifts and needs periodic refresh. The amplifier scales the held signal to a high-voltage output. The output is unipolar, meaning it operates from 0 V upward rather than swinging negative.

Design targets

High-voltage supply rail: 125–300 V
Required low-voltage rails: +6.0 to +7.5 V and −6.5 to −4.5 V; both required in addition to the HV rail
Output range: 0 V to HV rail − 5 V (up to 295 V at a 300 V rail)
Nominal voltage gain: 72 V/V
Capacitive load: 0–3 nF per output
Slew rate, no load: 2.2 V/µs rising, 2.0 V/µs falling
Operating temperature: −10 to +85 °C

Practical operating notes

Design scope covers the sample-and-hold and high-voltage amplifier circuits. Channel-selection logic and shared output-current-limit controllers are outside this design scope.
The high-voltage rail and both low-voltage supply rails are required. Up to 295 V output requires a 300 V high-voltage rail; it is not available across the whole supply range.
The input is arranged around 0–4.096 V. The usable output depends on supply headroom, so the entire input span is not linear at lower high-voltage rails.
The rising and falling slew targets apply with no load. They do not specify performance at 3 nF. Available drive current, load capacitance and thermal limits must be assessed for the application.
Held voltages gradually drift. Periodic refresh is needed; no output-settling or refresh-rate guarantee is specified here.

Possible applications

Capacitive MEMS (microelectromechanical systems, tiny mechanical devices made with chip-fabrication methods)
Piezoelectric positioning and actuation
Optical MEMS switching

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