High linearity digital variable gain amplifier
View Patent ↗Variable gain amplifiers offering high frequency response with improved linearity and reduced power dissipation are provided. An amplifier is disclosed that is constructed from a one-stage topology with multiple signal paths and compensation networks for improved linearity and stable operation. In this amplifier, improved performance is obtained by replacing single transistor components with enhanced active devices which incorporate local negative feedback. One embodiment of the invention is a transconductance enhancement circuit that improves transconductance and input impedance relative to the prior art. A further development is an enhanced active cascode circuit that provides improved linearity. A high frequency bipolar transistor switch is also disclosed that incorporates lateral PNP transistors as high frequency switches with improved OFF-state to ON-state impedance ratio to realize a variable gain function. These circuits are combined in an amplifier circuit that provides variable gain and high frequency performance, with improved linearity, gain, and input impedance.
1. A method of operating a transistor switch arranged in an integrated circuit, the transistor switch having a first semiconductor region of a first conductivity type, and an array of semiconductor wells formed in the first semiconductor region, the array including multiple first wells of a second conductivity type and multiple second wells of the second conductivity type, at least one of the first wells being surrounded from four sides with the second wells, the first wells being electrically connected with each other to provide a first terminal of the transistor switch, the second wells being electrically connected with each other to provide a second terminal of the transistor switch, the first semiconductor region providing a third terminal of the transistor switch; the integrated circuit having an input node, a ring region of the second conductivity type surrounding the array and connected to the first semiconductor region, and a second semiconductor region of the second conductivity type beneath the first semiconductor region, the method comprising the steps of:
providing current via the input node to turn the switch ON,
forward-biasing all first and second wells when the switch is ON, and
controlling the current injected into the second semiconductor region using the ring region connected to the first semiconductor region so as to enable the switch to operate in an ON state.
2. The method of claim 1 , wherein the transistor switch includes a bipolar transistor.
3. The method of claim 1 , wherein the first terminal is an emitter of the transistor switch, the second terminal is a collector of the transistor switch, and the first semiconductor region provides a base of the transistor switch.