Automatic gain control circuit of radio receiver
First Claim
1. An automatic gain control circuit of a radio data communication system using a spread spectrum method, comprising:
- a band pass filter for passing a desired frequency band of a signal received via an antenna of said radio data communication system;
low noise amplifier for low noise amplifying an output of said band pass filter;
down converting means for generating an IF signal by down converting a frequency of an output of said low noise amplifier;
a limiter for generating a received signal strength voltage indicative of a received signal strength of said IF signal;
demodulation means for producing a first control signal, a second control signal and demodulated data by demodulating said IF signal;
a comparator for comparing said received signal strength indicator voltage with a given reference voltage;
a D flip-flop having a data input terminal connected to an output terminal of said comparator, a clock terminal connected to receive said first control signal, a reset terminal connected to receive said second control signal and a Q output terminal for outputting a signal applied to said data terminal in response to a leading edge of said first control signal;
an AND gate having a first terminal connected to said Q output terminal of said D flip-flop and a second terminal connected to receive said first control signal; and
a field effect transistor having a gate for receiving an output of said AND gate, a drain provided with a given voltage, and source connected to a power supply terminal of said low noise amplifier through a resistor.
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Accused Products
Abstract
An automatic gain control circuit which is digitally embodied to prevent deterioration of bit error rate generated by saturation of a low noise amplifier located at the front stage of a receiver through an input of high power to an antenna, thereby simplifying construction thereof and improving commercialization. The automatic gain control circuit of a radio data communication system using a spread spectrum method utilizes a low noise amplifier for low noise amplifying a bandpass filtered signal received through an antenna; a limiter for generating a received signal strength indicator voltage in order to constantly maintain the signal received as a local oscillation frequency through the antenna before downward frequency conversion; a unit for separating the a signal transmitted through the limiter to I and Q channels; a comparator for comparing the received signal strength indicator voltage with a given reference voltage; a D flip-flop for inputting an output of the comparator applied to a data input terminal in synchronization to a given first control signal; an AND gate for ANDing the output of the D flip-flop and the first control signal; a field effect transistor having a gate for receiving the output of the AND gate therein, a drain provided with a given voltage, and source connected to power supply terminal of the low noise amplifier through a resistor; and, a modem for sensing carrier, generating the sensed signal as the first control signal, and outputting digital demodulation data from a signal separated to the I and Q channels.
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Citations
13 Claims
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1. An automatic gain control circuit of a radio data communication system using a spread spectrum method, comprising:
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a band pass filter for passing a desired frequency band of a signal received via an antenna of said radio data communication system; low noise amplifier for low noise amplifying an output of said band pass filter; down converting means for generating an IF signal by down converting a frequency of an output of said low noise amplifier; a limiter for generating a received signal strength voltage indicative of a received signal strength of said IF signal; demodulation means for producing a first control signal, a second control signal and demodulated data by demodulating said IF signal; a comparator for comparing said received signal strength indicator voltage with a given reference voltage; a D flip-flop having a data input terminal connected to an output terminal of said comparator, a clock terminal connected to receive said first control signal, a reset terminal connected to receive said second control signal and a Q output terminal for outputting a signal applied to said data terminal in response to a leading edge of said first control signal; an AND gate having a first terminal connected to said Q output terminal of said D flip-flop and a second terminal connected to receive said first control signal; and a field effect transistor having a gate for receiving an output of said AND gate, a drain provided with a given voltage, and source connected to a power supply terminal of said low noise amplifier through a resistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An automatic gain control method for controlling a gain of a low noise amplifier located at the front stage of a receiver in a radio data communication system utilizing spread spectrum communications, said method comprising the steps of:
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band pass filtering a signal received through an antenna of said radio data communication system to produce a band pass filtered signal; applying said band pass filtered signal, via a low noise amplifier, to a frequency down converter to produce an IF signal; passing said IF signal through a limiter to a demodulator; demodulating said IF signal passed through said limiter to produce demodulated data, a first control signal and a second control signal; outputting a received signal strength indicator voltage from said limiter; comparing said received signal strength indicator voltage to a reference voltage; turning off said low noise amplifier when said received signal strength indicator voltage is greater than said reference voltage and in sync with said first control signal. - View Dependent Claims (10, 11, 12, 13)
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Specification