Variable gain amplifier

#1. Technical Field

#This invention relates to the field of variable gain amplifiers. In particular, the invention relates to variable gain amplifiers for low voltage and high frequency operation.

#2. Description of the Prior Art

#FIG. 1A is a schematic diagram of a variable gain amplifier in accordance with the present invention;

#FIG. 1B is a graph showing the gains of amplifier stages in a variable gain amplifier in accordance with the present invention;

#FIG. 2 is a diagram of an implementation of a variable gain amplifier in accordance with the present invention;

#A basic variable gain amplifier (VGA) architecture 100 is shown in FIG. 1A. The VGA 100 employs a multipath amplifier arrangement. A first amplifier 101 uses a full size input signal 103 and a second amplifier 102 uses an attenuated form 104 of this input signal 103. A resistor input network 105 is used to attenuate the input signal 103 to provide the attenuated form 104 for the input signal to the second amplifier 102. In place of a resistor input network, a line termination or a parallel divider network could be used.

#Each of the first and second amplifiers 101, 102 has a gain adjustment means 107, 108 which is controlled by a gain control network 106. The outputs 113, 114 of the first and second amplifiers 101, 102 are summed by summer 110 to provide the overall output 112 of the VGA 100.

#At low gain settings which cover the gain range where the VGA 100 is attenuating, the second amplifier 102 using the attenuated form 104 of the input signal 103 is active with the first, full signal amplifier 101 disabled.