Avalanche Transistor Pulser for Fast-Gated Operation of Microchannel Plate Image-Intensifiers
Citation
Lundy, A., Parker, J. R., Lunsford, J. S., & Martin, A. D. (1977). Avalanche Transistor Pulser for Fast-Gated Operation of Microchannel Plate Image-Intensifiers. IEEE Transactions on Nuclear Science, NS-24, 2.
Keywords
- Avalanche Transistor
- Fast-Gated Operation
- Microchannel Plate Image Intensifier (MCPI)
- High-Speed Photography
- Pulse Characteristics
- Circuit Design
- Performance and Limitations
- Divider Network
Brief
This article details the design and performance of an avalanche transistor pulser used for fast-gated operation of a microchannel plate image intensifier.
Summary
The article details the design and performance of an avalanche transistor pulser used to operate a microchannel plate image-intensifier (MCPI) tube for high-speed photography.
- The MCPI tube is shuttered by applying a +270 volt pulse to its input gap, which is normally back-biased with -90 volts.
- Due to the high cost of the tubes, a line-type pulser with limited stored energy is used to prevent tube damage from pulser malfunction.
- The pulser utilizes 2N3700 avalanche transistors in series to generate 1000 volt pulses with rise and fall times of less than 5 ns.
- The transistors are mounted on hybrid substrates to reduce circuit inductance and improve rise time.
- A mixer-attenuator circuit reduces the pulse amplitude to 270 volts before it is applied to the MCPI tube.
- A divider network provides DC operating voltages and control of transient voltages on the MCPI tube, including programmable gain control in "f-stop" steps.
- The system achieves an effective exposure time of 15 ns with a resolution of 17 to 19 line pairs/mm.
- The authors also discuss various challenges encountered during the development process:
- Limited availability of transistors suitable for avalanche mode operation and lack of reliable data on their performance characteristics.
- Triggering stability issues with different biasing schemes and transistor configurations.
- Impedance mismatch between the pulser and the capacitive load of the MCPI tube, requiring careful cable selection and minimization of inductance.
- Transient voltage spikes across the MCPI tube during turn-on and turn-off, necessitating the use of zener diodes for protection.
- Reliability concerns regarding capacitors in the divider network, addressed by using high-reliability components with special testing.
- Limited lifetime of the 2N3700 transistors when generating longer pulses at high currents.