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[[Image:S20photocathode_QE.jpg|frame|HPD Photo-cathode efficiency as a function of wavelength.]]
[[Image:S20photocathode_QE.jpg|frame|HPD Photo-cathode efficiency as a function of wavelength.]]
The quantum efficiency of this device is shown in the adjacent figure. The DEP-supplied device provides a gain factor of 2700 at the HV of 12 kV and additionally requires 40 - 80 V bias to collect the electrons across the diode junction. Built into the package is a transimpedance amplifier with 50 kΩ || 1.5 pF feedback, requiring ±5 V supplies. The amplifier circuit also contains a 51.1 Ω resistor in series with the output. Reading out the HPD signal from the amplifier with 50 Ω termination creates a factor of two (50 Ω/(50 Ω + 51.1 Ω)) on top of the 50 kΩ current to voltage conversion.
The quantum efficiency of this device is shown in the adjacent figure. The DEP-supplied device has an inherent capacitance (C<sub>HPD</sub>) of 200 F and provides a gain factor of 2700 at the HV of 12 kV and additionally requires 40 - 80 V bias to collect the electrons across the diode junction. Built into the package is a transimpedance amplifier with 50 kΩ || 1.5 pF feedback, requiring ±5 V supplies. The amplifier circuit also contains a 51.1 Ω resistor in series with the output. Reading out the HPD signal from the amplifier with 50 Ω termination creates a factor of two (50 Ω/(50 Ω + 51.1 Ω)) on top of the 50 kΩ current to voltage conversion.