Bleeder powered gating amplifier
A gating circuit switches the responsivity of a photomultiplier tube between ON and OFF states by modulating the voltage bias of the one or more of its electrodes. The gating circuit capacitively couples a voltage pulse to the photocathode or other electrode of the photomultiplier tube in response to a low-voltage gating triggering signal. The voltage divider network and high-voltage power supply used to statically bias the photomultiplier tube also power the gating circuitry and source the gating voltage pulse, thus circumventing the need for a separate high-voltage power supply. The gating circuit represents a near-inconsequential burden on the power supply, as it draws practically negligible current from the voltage divider network. The electrode gating pulse characteristics, including rise- and fall-times, voltage swing amplitude and duration, can be modified by adjusting resistor and capacitor values and Zener diode characteristics of the gating circuit and voltage divider network. The circuit can also be used to gate related devices such as microchannel plates and image intensifiers.
1. Apparatus for providing a modulated signal in response to incident radiation comprising:
means responsive to incident radiation for emitting electrons in response to such radiation;
electron multiplication means disposed for receiving the electrons emitted by said radiation responsive means and multiplying said electrons;
an anode disposed for receiving the multiplied electrons and providing an electrical signal in response thereto;
a voltage divider network connected to said electron multiplication means for providing a biasing voltage thereto when connected to a high voltage power supply; and
a gating circuit operatively connected to said radiation responsive means, said voltage divider network, and an external input signal source, said gating circuit being adapted for providing a gating signal to said radiation responsive means in response to an input signal from said external input signal source, whereby said apparatus can be modulated between respective ON and OFF states; said gating circuit comprising:
voltage level shifting means operatively connected to receive the external input signal and for providing a voltage level shifted output signal in response to the external input signal; and
a switching circuit operatively connected between said voltage divider network and ground and to said voltage level shifting means, said switching circuit being adapted for providing the gating signal to the radiation responsive means.
2. An apparatus as set forth in claim 1 wherein the radiation responsive means comprises a photocathode.
3. An apparatus as set forth in claim 1 comprising a current amplifier operatively connected between said voltage level shifting means and said switching circuit.
4. Apparatus as set forth in claim 1 wherein said electron multiplication means comprises a dynode having a secondary electron emissive surface.
5. Apparatus as set forth in claim 4 wherein said electron multiplication means comprises a plurality of dynodes each having a secondary electron emissive surface.
6. Apparatus as set forth in claim 1 wherein said electron multiplication means comprises a microchannel plate.
7. Apparatus as set forth in claim 6 wherein said electron multiplication means comprises a second microchannel plate.
8. Apparatus for providing a modulated signal in response to incident radiation comprising:
means responsive to incident radiation for emitting electrons in response to such radiation;
electron multiplication means disposed for receiving the electrons emitted by said radiation responsive means and multiplying said electrons;
an anode disposed for receiving the multiplied electrons and providing an electrical signal in response thereto;
a voltage divider network connected to said electron multiplication means for providing a biasing voltage thereto when connected to a high voltage power supply; and
a gating circuit operatively connected to said radiation responsive means, said voltage divider network, and an external input signal source, said gating circuit being adapted for providing a gating signal to said radiation responsive means in response to an input signal from said external input signal source, whereby said apparatus can be modulated between respective ON and OFF states; said gating circuit comprising:
voltage level shifting means operatively connected to receive the external input signal and for providing two voltage level shifted output signals in response to the external input signal; and
a logic circuit operatively connected between said voltage divider network and ground and to said voltage level shifting means, said logic circuit being adapted for providing the gating signal to the radiation responsive means.
9. An apparatus as set forth in claim 8 comprising first and second current amplifiers operatively connected between said voltage level shifting means and said logic circuit.
10. Apparatus for providing a modulated signal in response to incident radiation comprising:
a photocathode responsive to incident radiation for emitting electrons in response to such radiation;
electron multiplication means disposed for receiving the electrons emitted by said photocathode and multiplying said electrons;
an anode disposed for receiving the multiplied electrons and providing an electrical signal in response thereto;
a voltage divider network connected to said photocathode and said electron multiplication means for providing a biasing voltage thereto when connected to a high voltage power supply; and
a gating circuit operatively connected to said electron multiplication means, said voltage divider network, and an external input signal source, said gating circuit being adapted for providing a gating signal to said electron multiplication means in response to an input signal from said external input signal source, whereby said apparatus can be modulated between respective ON and OFF states; said gating circuit comprising
voltage level shifting means operatively connected to receive the external input signal and for providing a voltage level shifted signal in response to the external input signal; and
a transistor switch operatively connected between said voltage divider network and ground and to said voltage level shifting means, said transistor switch being adapted for providing the gating signal to the electron multiplication means.
11. An apparatus as set forth in claim 10 comprising a current amplifier operatively connected between said voltage level shifting means and said transistor switch.
12. Apparatus as set forth in claim 10 wherein said electron multiplication means comprises a dynode having a secondary electron emissive surface.
13. Apparatus as set forth in claim 12 wherein said gating circuit is operatively connected to said dynode.
14. Apparatus as set forth in claim 12 wherein said electron multiplication means comprises a plurality of dynodes each having a secondary electron emissive surface.
15. Apparatus as set forth in claim 14 wherein said gating circuit is operatively connected to at least one of said plurality of dynodes.
16. Apparatus as set forth in claim 10 wherein said electron multiplication means comprises a microchannel plate.
17. Apparatus for providing a modulated signal in response to incident radiation comprising:
a photocathode responsive to incident radiation for emitting electrons in response to such radiation;
electron multiplication means disposed for receiving the electrons emitted by said photocathode and multiplying said electrons;
an anode disposed for receiving the multiplied electrons and providing an electrical signal in response thereto;
a voltage divider network connected to said photocathode and said electron multiplication means for providing a biasing voltage thereto when connected to a high voltage power supply; and
a gating circuit operatively connected to said electron multiplication means, said voltage divider network, and an external input signal source, said gating circuit being adapted for providing a gating signal to said electron multiplication means in response to an input signal from said external input signal source, whereby said apparatus can be modulated between respective ON and OFF states; said gating circuit comprising:
voltage level shifting means operatively connected to receive the external input signal and for providing two voltage level shifted output signals in response to the external input signal; and
a transistor-transistor logic circuit operatively connected between said voltage divider network and ground and to said voltage level shifting means, said transistor-transistor logic circuit being adapted for providing the gating signal to the electron multiplication means.
18. An apparatus as set forth in claim 17 comprising first and second current amplifiers operatively connected between said voltage level shifting means and said transistor-transistor logic circuit.