Video preamplifier for laser systems
AssigneeMartin Martietta Corporation
InventorsTien W. Chu, Thomas W. Holland
Life of this patent
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Abstract
An automatic gain controlled preamplifier for use with a laser detector and having a wide bandwidth and a low-noise figure. The preamplifier includes a voltage controlled input attenuator stage feeding a low noise wideband amplifier stage which drives an output amplifier stage. Each stage has independent AGC drivers which permit sequential control of the three stages by AGC voltages of different ranges. The output stage is controlled for low level signals, the attenuator stage for medium level signals, and the low noise stage by large signals, thereby maintaining the low noise characteristic for weak signals. The preamplifier is implemented in form for production as a monolithic circuit.
Claims18
A gain controlled low noise preamplifier having a large dynamic range comprising:
- output amplifier means having a signal input, a signal output, and a gain control voltage input, said output amplifier means having its gain reduced by an external dc voltage applied to said gain control input as said external voltage increases from essentially zero to a first preselected value, said reduction in gain proportional to said applied external dc voltage;
- attenuator means having a pair of input terminals and a pair of output terminals, each of said pairs having a common ground terminal, said input terminals for receiving an input signal, said attenuator means having a gain control voltage input and having its attenuation increased by said external dc voltage applied to said attenuation control input only when said external voltage increases from said first preselected value to a second preselected value, said attenuator means thereby reducing the amplitude of the input signal appearing at said output terminals over a range proportional to the value of said external dc voltage between said first preselected value and said second preselected value;
- and
- low noise amplifier means having a signal input connected to said output terminals of said attenuator means, a signal output connected to said signal input of said output amplifier means, and a gain control input for receiving said external voltage when the magnitude thereof is greater than said second preselected value, the gain of said low noise amplifier means being reduced as said external voltage increases from said second preselected value, said gain reduction proportional to the magnitude of said external dc voltage;
- wherein said external dc voltage is proportional to the magnitude of said input signal, and said reductions in gain of said preamplifier do not significantly reduce the noise figure of said preamplifier.
In a missile control system having a dc control voltage generating means for producing a dc automatic gain control voltage proportional to the magnitude of an input signal, a preamplifier for amplifying said input signal, said preamplifier having a low noise characteristic over a wide dynamic range, comprising:
- attenuator means for receiving said input signal;
- low noise amplifier means connected to receive the input signals from said attenuator means;
- output amplifier means for receiving the amplified signals from said low noise amplifier means;
- first automatic gain control driver means connected to said output amplifier for controlling the gain of said output amplifier proportional to the magnitude of said dc automatic gain control voltage only when said input signal is within a first amplitude range representative of a weak input signal level range;
- second automatic gain control driver means connected to said attenuator means for increasing attenuation of said attenuator to said input signal only when the amplitude of said input signal is within a second amplitude range having a minimum amplitude greater than the highest amplitude of said first amplitude range;
- and
- third automatic gain control driver means connected to said low noise amplifier means for reducing the gain of said low noise amplifier means when the amplitude of said input signal is greater than the highest amplitude of said second amplitude range;
- wherein the noise contribution of said low noise amplifier is negligible when the amplitude of said input signal is greater than the highest amplitude of said first amplitude range.
Dependencies are inferred from the claim text.