US 2004/0061554 A1 · Variable gain amplifier for use in communications

Abstract

A variable gain amplifier of low amplitude distortion, and low noise, having a large variable range, is provided. A variable gain differential amplifier that controls a gain by use of bias current is used as each of unit amplifiers (VGAs) making up the variable gain amplifier. A large variable gain range is obtained by series-connecting a plurality of the variable gain differential amplifiers. An attenuator is installed on the input side of the unit amplifier (VGA) at least in the initial stage. By doing so, it becomes possible to prevent amplitude distortion from occurring to the respective VGAs. An attenuator utilizing voltage division by capacitors, generating no noise, is used for lowering noise. Further, the variable gain amplifier is provided with a fixed gain amplifier installed in the final stage as necessary in order to obtain a total gain as desired. With the use of the variable gain amplifier as a variable gain amplifier for output power control of a polar loop transmitter, an excellent function for output power control can be achieved without causing significant deterioration in distortion characteristic and noise characteristic thereof.

Claims20

Dependent claims

A variable gain amplifier having a multiple-stage configuration, the variable amplifier comprising:

a plurality of variable gain unit amplifiers connected in series, wherein the plurality of variable gain unit amplifiers are configured to obtain a large variable gain range for the variable gain amplifier, wherein each of the plurality variable gain unit amplifiers has a differential input side;
and
a plurality of low noise attenuators, wherein each of the plurality of low noise attenuators is connected to the differential input side of each of the plurality of variable gain unit amplifiers.

A polar loop transmitter comprising:

a modulator configured to output a modulated signal;
an amplitude loop having an amplitude comparator;
a phase loop having a phase comparator;
and
a down-convert mixer configured to convert a frequency of a feedback signal detecting an output of a power amplifier into an intermediate frequency band and thereby further configured to output an intermediate frequency signal, wherein the amplitude comparator is configured to compare an amplitude component of the modulated signal with an amplitude component of the intermediate frequency signal such that the amplitude loop is configured to provide amplitude feedback to a control terminal, wherein the phase comparator is configured to compare a phase component of the modulated signal with a phase component of the intermediate frequency signal such that the phase loop is configured to provide phase comparisons to a transmission voltage control oscillator, wherein the transmission voltage control oscillator is thereby configured to input a transmission signal that is phase-modulated to the power amplifier, wherein the polar loop transmitter is configured to transmit the transmission signal after amplification by the power amplifier;
and
a variable gain amplifier connected between the down-convert mixer, the amplitude comparator, and the phase comparator, wherein the variable gain amplifier is configured to facilitate output power control of the power amplifier.

4 more elements

Dependencies are inferred from the claim text.

Variable gain amplifier for use in communications

Life of this patent

Variable gain amplifier for use in communications

Life of this patent

Abstract

Claims20