Invention Grant
- Patent Title: Variable gain amplifiers with output phase invariance
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Application No.: US16037310Application Date: 2018-07-17
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Publication No.: US10924075B2Publication Date: 2021-02-16
- Inventor: Sriram Muralidharan
- Applicant: ANALOG DEVICES, INC.
- Applicant Address: US MA Norwood
- Assignee: ANALOG DEVICES, INC.
- Current Assignee: ANALOG DEVICES, INC.
- Current Assignee Address: US MA Norwood
- Agency: Knobbe, Martens, Olson & Bear, LLP
- Main IPC: H03G3/10
- IPC: H03G3/10 ; H03G3/30 ; H03F1/32 ; H03F3/19 ; H04B1/40

Abstract:
Variable gain amplifiers (VGA) with output phase invariance are provided herein. In certain embodiments, a VGA is operable in a selected gain setting chosen from multiple gain settings that provide different amounts of amplification to a radio frequency (RF) input signal. The VGA includes a gain transistor that has a substantially constant bias current across the gain settings, such that the VGA's output phase, input impedance matching, and/or input return loss are substantially constant. The gain setting of the VGA is selected by controlling relative biasing of a pair of cascode transistors each connected to the gain transistor by a corresponding degeneration resistor. The degeneration resistors provide compensation that reduces or eliminates a difference in output phase of the VGA across gain settings, for instance, by introducing a zero in a transfer function of the VGA that cancels a pole arising from the cascode transistors.
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