Baseband circuit incorporated in direct conversion receiver free from direct-current offset voltage without change of cut-off frequency
First Claim
1. A base band circuit for producing an output base band signal from an input base band signal, comprising:
- a first low pass filter circuit supplied at an input port thereof with said input base band signal for restricting a frequency band of said input base band signal, and outputting a filtrate signal from an output port thereof, a series of variable gain amplifiers forming a series circuit together with said first low pass filter, and responsive to an internal gain control signal indicating a gain to be achieved so as to produce said output base band signal from said filtrate signal at an output port of said series circuit through an amplification at said gain; and
a feedback loop connected between said output port of said series circuit and an input port of said series circuit, and including a direct current component extracting circuit attenuating said output base band signal with an attenuation factor corresponding to said gain and extracting a direct current component from said output base band signal and an eliminating circuit eliminating said direct current component from said input base band signal.
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Accused Products
Abstract
A base band circuit forms a part of an automatic gain controller incorporated in a direct conversion receiver, and includes a series of variable gain amplifiers controlled by a gain controller and a feedback loop connected between the output node and the input node of the series of variable gain amplifiers, wherein the feedback loop has an attenuation circuit connected between the output node of the series of variable gain amplifiers and an inverted integrating circuit which, in turn, is connected through an adder and a low pass filter to the input node of the series of variable gain amplifiers so that direct current offset voltage is eliminated from the output signal of the series of variable gain amplifiers without change of cut-off frequency.
101 Citations
14 Claims
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1. A base band circuit for producing an output base band signal from an input base band signal, comprising:
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a first low pass filter circuit supplied at an input port thereof with said input base band signal for restricting a frequency band of said input base band signal, and outputting a filtrate signal from an output port thereof, a series of variable gain amplifiers forming a series circuit together with said first low pass filter, and responsive to an internal gain control signal indicating a gain to be achieved so as to produce said output base band signal from said filtrate signal at an output port of said series circuit through an amplification at said gain; and
a feedback loop connected between said output port of said series circuit and an input port of said series circuit, and including a direct current component extracting circuit attenuating said output base band signal with an attenuation factor corresponding to said gain and extracting a direct current component from said output base band signal and an eliminating circuit eliminating said direct current component from said input base band signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification