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US 5,311,088 AGranted
Transconductance cell with improved linearity
AssigneeAT&T Bell Laboratories
InventorDale H. Nelson
Life of this patent
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AssigneeAT&T Bell Laboratories
InventorDale H. Nelson
Estimating the term…
Analog filters may be conveniently implemented in MOS technology by the use of "transconductance cells". Each cell includes stages each having a pair of current paths, with each path comprising a current source and input transistor. The gain of each stage is set by a transistor connected across the current path, with the transconductance of this transistor being controlled by its gate voltage. In the inventive technique, a transconductance cell comprising two input stages utilizes inputs to each input stage that are in-phase rather than complementary, as in prior-art designs. The inputs to the second input stage are then each balanced (out of phase) with respect to the inputs to the first input stage. Higher linearity is obtained, with the common-mode signal being cancelled by the summation of currents supplied by the input stages to the common output stage. A biquadratic filter conveniently implements this technique, with other applications being possible.
A circuit employing first and second input stages and an output stage, each input stage having first and second current paths each comprising a current source connected in series with a signal input transistor coupled to said output stage, and each input stage having a controlled transconductance transistor connected between the first and second current paths,
An integrated circuit comprising a biquadratic filter comprising a first cell and a second cell, with each cell having first and second non-inverting inputs (AP, BP), first and second inverting inputs (AN, BN), a non-inverting output (OP), and an inverting output (ON);
An integrated circuit comprising a biquadratic filter comprising a first cell and a second cell, with each cell having a first input stage, a second input stage, and an output stage:
Dependencies are inferred from the claim text.