High swing operational transconductance amplifier
First Claim
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1. A differential amplifier, comprising:
- a voltage supply having first and second supply terminals;
a first pair of input transistors;
a second pair of input transistors complementary with the first pair;
first and second current sources for biasing the first and second pair of input transistors, respectively;
first and second load circuits for decreasing, respectively, the bias current supplied by the first and second current sources;
wherein the first input pair turns off when a common mode input voltage becomes close to a voltage on the first supply terminal, and the second input pair turns off when a common mode input voltage becomes close to a voltage on the second supply terminal; and
wherein the second load circuit ceases to decrease the bias current supplied by the first source when the common mode input voltage becomes close to the voltage on the first supply terminal, and wherein the first load circuit ceases to decrease the bias current supplied by the second source when the common mode input voltage becomes close to the voltage on the second supply terminal, whereby the transconductance of the differential amplifier remains relatively constant.
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Abstract
A differential input stage for an operational transconductance amplifier is provided with complementary input transistor pairs. For each pair, a diode dummy load is provided. When the common mode input signal is near the positive or negative supply voltage, one of the pairs turns off. The diode loads act to increase the current through the other pair when this occurs. This results in the provision of a constant transconductance over the entire common mode input range.
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Citations
13 Claims
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1. A differential amplifier, comprising:
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a voltage supply having first and second supply terminals; a first pair of input transistors; a second pair of input transistors complementary with the first pair; first and second current sources for biasing the first and second pair of input transistors, respectively; first and second load circuits for decreasing, respectively, the bias current supplied by the first and second current sources; wherein the first input pair turns off when a common mode input voltage becomes close to a voltage on the first supply terminal, and the second input pair turns off when a common mode input voltage becomes close to a voltage on the second supply terminal; and wherein the second load circuit ceases to decrease the bias current supplied by the first source when the common mode input voltage becomes close to the voltage on the first supply terminal, and wherein the first load circuit ceases to decrease the bias current supplied by the second source when the common mode input voltage becomes close to the voltage on the second supply terminal, whereby the transconductance of the differential amplifier remains relatively constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification