Comparator unit for a flash analog-to-digital converter
First Claim
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1. A comparator unit for a flash A/D converter having a plurality of comparator units and an encoder ROM, each said comparator unit comprising:
- switching transistors which switch conductive states based upon a clock input signal;
comparing transistors having a single output for comparing an input voltage to a reference voltage, said comparing transistors having their output connected to one of said switching transistors;
latching transistors for latching the output voltage of the comparing transistors, said latching transistors being connected to said comparing transistors and said switching transistors and latch based upon the input clock signal;
miller-capacitance reducing means for reducing a miller capacitance effect of said latching transistors, said miller effect reducing means comprising a pair of transistors having a constant d.c. power input and whose output is connected to said latching transistors and said comparing transistors;
first and second signal transistors being connected to said miller-capacitance reducing means and said latching transistors for generating a signal to an output means; and
said output means outputting said compared output voltage to an encoder ROM based upon the comparison of the input voltage and the reference voltage.
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Abstract
A high speed comparator unit for a flash A/D converter in which a bank of comparator units compare simultaneously an analog input voltage with equally spaced reference voltages, and an encoder ROM produces digital signals based on the comparator unit'"'"'s outputs. The comparator unit includes a two-stage cascode configuration and a level shifter configuration which effectively reduces the miller-effect of the comparator unit.
159 Citations
7 Claims
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1. A comparator unit for a flash A/D converter having a plurality of comparator units and an encoder ROM, each said comparator unit comprising:
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switching transistors which switch conductive states based upon a clock input signal; comparing transistors having a single output for comparing an input voltage to a reference voltage, said comparing transistors having their output connected to one of said switching transistors; latching transistors for latching the output voltage of the comparing transistors, said latching transistors being connected to said comparing transistors and said switching transistors and latch based upon the input clock signal; miller-capacitance reducing means for reducing a miller capacitance effect of said latching transistors, said miller effect reducing means comprising a pair of transistors having a constant d.c. power input and whose output is connected to said latching transistors and said comparing transistors; first and second signal transistors being connected to said miller-capacitance reducing means and said latching transistors for generating a signal to an output means; and said output means outputting said compared output voltage to an encoder ROM based upon the comparison of the input voltage and the reference voltage. - View Dependent Claims (2, 3)
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4. A comparator unit for a flash A/D converter comprising:
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a first switch transistor having a base connected to a clock signal, a collector, and an emitter; a second switch transistor having a base connected to an inverted clock signal, a collector, and an emitter; a pair of comparing transistors having their bases connected to voltage signals to be compared, collectors, and emitters connected to the collector of said first switch transistor; a first latch transistor having a base, a collector connected to the collector of one of said comparing transistors, and an emitter connected to the collector of said second switch transistor; a second latch transistor having a base, a collector connected to the collector of another of said comparing transistors, and an emitter connected to the collector of said second switch transistor; a first resistor and a second resistor each having a first terminal and a second terminal; a first signal transistor having a base connected to a first voltage source, a collector connected to an enable line of a first adjacent comparator unit, and an emitter connected to a second terminal of said first resistor; a second signal transistor having a base connected to the first voltage source, a collector connected to an enable line of a second adjacent comparator unit, and an emitter connected to a second terminal of said second resistor; a third resistor having a first terminal connected to the collector of said second signal transistor and a second termial connected to a voltage supply; a third signal transistor having a base connected to the collector of said second signal transistor, a collector connected to the voltage supply, and an emitter connected to an output; and a miller-capacitance reducer, having a plurality of transistors, each of the transistors being connected to at least one of the collectors of said comparing transistors, the base of said first and second latch transistors, and the first terminal of said first and second resistors. - View Dependent Claims (5, 6, 7)
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Specification