David C Rahn

US Patent:

20060164164, Jul 27, 2006

Filed:

Jan 12, 2005

Appl. No.:

11/034224

Inventors:

John Rogers - Ottawa, CA
David Rahn - Greensboro NC, US
A. Moore - Carp, CA

International Classification:

H03F 1/14
H03F 3/45

US Classification:

330252000, 330292000

Abstract:

A VGA is provided that is designed to reduce or even eliminate entirely variations in phase response/shift with changes in gain. Compensation is made for parasitic capacitances of elements in the VGA that would otherwise cause variation in phase with changes in gain. An additional capacitance is introduced to the VGA to compensate for the sources of the parasitic capacitance. The technique for introducing the additional capacitance depends on the source of the parasitic capacitance being treated. The additional capacitance is introduced to one or more of transistor amplifier circuits in the VGA, wherein each transistor amplifier circuit has a different gain and one of the transistor amplifier circuits is selected depending on the desired gain of the VGA. These compensation techniques equalize the phase response of the transistor amplifier circuits (each having a different gain) so that regardless of which transistor amplifier circuit is selected, the phase shift will be substantially the same. These techniques may be applied to each VGA stage of a multi-stage VGA system.