| US 7,592,869 B2 | ||
| Variable gain amplifier having dual gain control | ||
| Hyeon Min Bae, Champaign, Ill. (US); Naresh Ramnath Shanbhag, Champaign, Ill. (US); and Jonathan B. Ashbrook, Homer, Ill. (US) | ||
| Assigned to Finisar Corporation, Sunnyvale, Calif. (US) | ||
| Filed on Sep. 17, 2007, as Appl. No. 11/856,681. | ||
| Prior Publication US 2009/0072904 A1, Mar. 19, 2009 | ||
| Int. Cl. H03F 3/45 (2006.01) | ||
| U.S. Cl. 330—254 [330/283; 330/300] | 16 Claims |
| 1. An electronic amplifier circuit comprising:
a differential amplifier having a pair of transistors accepting a differential input signal at base nodes of the transistor
pair;
a degeneration resistance coupled between emitters of the pair of transistors, the degeneration resistance comprising a first
field effect transistor (FET);
a load resistance coupled between collectors of the pair of transistors, the load resistance comprising a second FET; and,
a control circuit for increasing the gain factor of the differential amplifier by decreasing the degeneration resistance and
increasing the load resistance
wherein the control circuit receives a desired gain control signal and responsively generates a first gate-voltage control
signal for controlling the degeneration resistance and generates a second gate-voltage control signal for controlling the
load resistance; and
wherein the control circuit converts the desired gain control signal to a first and second current signal, and converts the
first and second current signal to the first gate-control voltage and the second gate-control voltage, respectively.
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