Constant transconductance bias circuit and method
First Claim
1. An integrated circuit comprising:
- a differential stage having a first differential pair of Field Effect Transistors (FETs) of a first conductivity type with a first bias current flowing therethrough and a second pair of differential FETs of a second conductivity type, electrically connected in parallel with the first pair of FETs, with a second bias current flowing therethrough; and
constant transconductance bias means, electrically connected to said differential stage, for monitoring one of the first and second bias currents and dynamically controlling the other of the first and second bias currents to maintain constant transconductance of said differential stage.
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Abstract
The reduction of the power supply voltage of VLSI circuits to 3.3 volts results in a significant loss in input and output swing in traditional CMOS analog circuits. In order to achieve rail-to-rail operation, n-channel and p-channel MOSFETs are placed in parallel so that at least one type of transistors are operating in a high gain region throughout the entire input range. However, circuit characteristics change as transistors turn on and off. A constant transconductance bias means enables the rail-to-rail CMOS differential stage to possess a constant transconductance over the entire common mode voltage range. Significantly, the bias circuit does not require any matching between the transistors of opposite types.
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Citations
22 Claims
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1. An integrated circuit comprising:
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a differential stage having a first differential pair of Field Effect Transistors (FETs) of a first conductivity type with a first bias current flowing therethrough and a second pair of differential FETs of a second conductivity type, electrically connected in parallel with the first pair of FETs, with a second bias current flowing therethrough; and constant transconductance bias means, electrically connected to said differential stage, for monitoring one of the first and second bias currents and dynamically controlling the other of the first and second bias currents to maintain constant transconductance of said differential stage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An integrated circuit comprising:
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differential input means including a plurality of transistors of a first conductivity type having a first device transconductance parameter and a plurality of transistors of a second conductivity type having a second device transconductance parameter which is different from said first device transconductance parameter, said first and second plurality of transistors defining a first input and a second input for receiving a first and a second input signal and at least one output for providing an output signal which is proportional to the difference between the first and second input signals; and constant transconductance bias means, electrically connected to said differential input means, for dynamically controlling the differential input means to maintain constant transconductance of the differential input means, notwithstanding the different device transconductance parameters of said first and second conductivity transistors. - View Dependent Claims (13)
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14. A method for operating an integrated circuit, the integrated circuit comprising a differential stage having a first differential pair of Field Effect Transistors (FETs) of a first conductivity type with a first bias current flowing therethrough and a second pair of differential FETs of a second conductivity type, electrically connected in parallel with the first pair of FETs, with a second bias current flowing therethrough, said method comprising the steps of:
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monitoring one of the first and second bias currents; and dynamically controlling the other of the first and second bias currents to maintain constant transconductance of the differential stage. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22)
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Specification