Temperature-compensated voltage level sense circuit
First Claim
1. A circuit for sensing the level of an input signal, comprising:
- a comparator, having first and second inputs;
an input leg, having an input coupled to an input terminal receiving the input signal, and coupled to the first comparator input, comprising;
an input capacitor;
a first switch, connected between the input terminal and said input capacitor;
a second switch, connected between the input capacitor and the first comparator input;
a first bias circuit comprising a bipolar transistor, for defining a first diode voltage;
a first charge-sharing capacitor;
a third switch, connected between the emitter of the bipolar transistor in said first bias circuit and said first charge-sharing capacitor; and
a fourth switch, connected between the first charge-sharing capacitor and said first comparator input; and
a reference leg, coupled to the second comparator input, comprising;
a second bias circuit, comprising a bipolar transistor, for defining a second diode voltage different from said first diode voltage;
a second charge-sharing capacitor;
a fifth switch, connected between the emitter of the bipolar transistor in said second bias circuit and said second charge-sharing capacitor; and
a sixth switch, connected between the second charge-sharing capacitor and said second comparator input;
wherein the difference between said first diode voltage and said second diode voltage increases with increasing temperature.
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Abstract
A voltage level sense circuit that has temperature compensation is disclosed. The circuit includes charge-sharing capacitors in each of an input leg and a reference leg. The charge-sharing capacitors are precharged to voltages that are integral multiples of the forward bias voltage drop across the base-emitter junction of a bipolar transistor. The bipolar transistors in the input leg differ from those in the reference leg, so that the difference in base-emitter on voltages increases with temperature. The increasing difference in base-emitter on voltage compensates for the decrease in the absolute value of the base-emitter on voltage with temperature. Voltage level sensing is accomplished by sampling the input voltage with a capacitor, charge-sharing the sampled voltage with one of the precharged charge-sharing capacitors, and coupling the charge-shared result to an input of a differential amplifier comparator. The second charge-sharing capacitor, after sharing its charge with another capacitor inserted for purposes of circuit matching, is coupled to the other input of the differential amplifier, and the comparison is performed.
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Citations
18 Claims
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1. A circuit for sensing the level of an input signal, comprising:
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a comparator, having first and second inputs; an input leg, having an input coupled to an input terminal receiving the input signal, and coupled to the first comparator input, comprising; an input capacitor; a first switch, connected between the input terminal and said input capacitor; a second switch, connected between the input capacitor and the first comparator input; a first bias circuit comprising a bipolar transistor, for defining a first diode voltage; a first charge-sharing capacitor; a third switch, connected between the emitter of the bipolar transistor in said first bias circuit and said first charge-sharing capacitor; and a fourth switch, connected between the first charge-sharing capacitor and said first comparator input; and a reference leg, coupled to the second comparator input, comprising; a second bias circuit, comprising a bipolar transistor, for defining a second diode voltage different from said first diode voltage; a second charge-sharing capacitor; a fifth switch, connected between the emitter of the bipolar transistor in said second bias circuit and said second charge-sharing capacitor; and a sixth switch, connected between the second charge-sharing capacitor and said second comparator input; wherein the difference between said first diode voltage and said second diode voltage increases with increasing temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 14, 15, 16, 17, 18)
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12. A method of sensing the level of an input signal, comprising:
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precharging a first charge-sharing capacitor to a voltage which is an integral multiple of a first diode voltage; precharging a second charge-sharing capacitor to a voltage which is an integral multiple of a second diode voltage, said second diode voltage having a different temperature coefficient than said first diode voltage such that the difference between said first and second diode voltages increases with increasing temperature; sampling the input voltage by connecting an input capacitor to receive the input signal; connecting the input capacitor to the first charge-sharing capacitor so that the charge on the input capacitor and the first charge-sharing capacitor is shared therebetween; and coupling the first charge-sharing capacitor and the second charge-sharing capacitor to first and second inputs of a comparator, respectively, to sense the differential voltage thereat. - View Dependent Claims (13)
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Specification