Amplifier circuit with a switching device to provide a wide dynamic output range
An amplifier circuit having an amplifier chain comprising an input port and output port with a plurality of interconnected gain stages positioned in between. The output of one interconnected gain stage provides an input to the next stage within the amplifier chain. The output port coupled to the plurality of interconnected gain stages such that the amplifier circuit output is generated from any one or more of the interconnected gain stages.
1. An amplifier circuit having a photomultiplier tube comprising a photocathode; an anode; a plurality of dynodes interconnected with one another and between the photocathode and the anode so that an output of one dynode provides an input to a next dynode within the photomultiplier tube; and a switching device having a first terminal coupled to an output of a constant current source and a second terminal operable to be selectively coupled to a respective output of any of the dynodes coupled between the photocathode and the anode such that an amplifier circuit output current representing a difference between an output of the constant current source and an output of a selected one of the dynodes is generated by the switching device switching the output between any one or more of the dynodes and the switching device switches between a respective dynode output current dependent upon a time period that an output current from the anode is in a saturated state.
2. The amplifier circuit according to claim 1 , wherein said amplifier circuit further comprises a series of voltage dividers operably coupled to respective dynodes so as to provide a variety of dynode currents.
3. The amplifier circuit according to claim 1 , wherein said amplifier circuit further comprises a current clipping mechanism, operably coupled to the plurality of interconnected dynodes and arranged to clip the output of each of the interconnected dynodes to a respective maximum output current.
4. The amplifier circuit according to claim 3 , wherein said amplifier circuit further comprises a combiner operably coupled to the current clipping mechanism to sum a number of clipped currents from a number of interconnected dynodes.
5. The amplifier circuit according to claim 1 , wherein said amplifier circuit further comprises an amplifier operably configured to receive inputs from sub-groups of said plurality of said dynodes, and amplifying a dynode current output from a sub-group to provide a rough tuning operation of the amplifier circuit output.
6. The amplifier circuit according to claim 5 , wherein said amplifier includes a reduction factor to clip the current output from the respective group of dynodes.
7. The amplifier circuit according to claim 1 , the amplifier circuit further comprising a memory device operably coupled to the plurality of interconnected dynodes for selecting one or more gain stages to provide the output current for the amplifier circuit.