Fast automatic gain control circuit and method for zero intermediate frequency receivers and radiotelephone using same
First Claim
1. A method for controlling gain of an amplifier in a radio receiver, the amplifier including a gain control input, the radio receiver including an automatic gain control capacitor and configured for coupling to an antenna, the method comprising the steps of:
- detecting radio frequency (RF) signals at the antenna, producing detected RF signals;
filtering the detected RF signals in a filter circuit, producing filtered signals;
detecting a signal level of the filtered signals;
when the signal level of the filtered signals exceeds a predetermined threshold, generating a timing pulse having a predetermined duration;
applying a precharge pulse to the automatic gain control capacitor to charge the automatic gain control capacitor to a predetermined voltage;
applying the predetermined voltage to the gain control input;
applying the precharge pulse to the gain control input during the predetermined duration of the timing pulse to reduce the gain of the amplifier to a preset level; and
thereafter, adjusting the gain of the amplifier to a gain which prevents saturation of the filter circuit.
4 Assignments
0 Petitions
Accused Products
Abstract
A method and apparatus provides control of the gain of an input amplifier (306) in a radio receiver (300), such as in a radiotelephone handset (104). The radio receiver (300) includes an automatic gain control circuit (318). The automatic gain control circuit (318) includes a timer circuit (370) which provides asynchronous, digital automatic gain control circuit to perform a coarse gain adjustment. The automatic gain control circuit (318) further includes an integrator (366) which provides analog automatic gain control for providing remaining needed gain regulation. The automatic gain control circuit (318) provides substantial reduction in input signal acquisition time for the radio receiver (300).
150 Citations
17 Claims
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1. A method for controlling gain of an amplifier in a radio receiver, the amplifier including a gain control input, the radio receiver including an automatic gain control capacitor and configured for coupling to an antenna, the method comprising the steps of:
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detecting radio frequency (RF) signals at the antenna, producing detected RF signals; filtering the detected RF signals in a filter circuit, producing filtered signals; detecting a signal level of the filtered signals; when the signal level of the filtered signals exceeds a predetermined threshold, generating a timing pulse having a predetermined duration; applying a precharge pulse to the automatic gain control capacitor to charge the automatic gain control capacitor to a predetermined voltage; applying the predetermined voltage to the gain control input; applying the precharge pulse to the gain control input during the predetermined duration of the timing pulse to reduce the gain of the amplifier to a preset level; and thereafter, adjusting the gain of the amplifier to a gain which prevents saturation of the filter circuit. - View Dependent Claims (2)
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3. A receiver for receiving radio frequency (RF) signals, the receiver comprising:
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a receiver input and a receiver output; an input amplifier having an input coupled to the receiver input, an output and a gain control input; a first mixer circuit having an input coupled to the output of the input amplifier and an output; a filter circuit having an input coupled to the output of the first mixer circuit and an output; a single sideband mixer having an input coupled to the output of the filter circuit and an output coupled to the receiver output; an automatic gain control circuit including; a signal level detector having an input coupled to the output of the single sideband mixer and an output; an integrator having an input coupled to the output of the signal level detector and an output coupled to the gain control input of the input amplifier; a comparator having a first input coupled to the output of the signal level detector, a second input for receiving a reference level and an output; and a timer circuit having an input coupled to the output of the comparator and an output coupled to the output of the integrator, the timer circuit providing to the output of the integrator a voltage pulse having a predetermined time duration in response to a trigger signal received from the output of the comparator. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10)
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11. An automatic gain control circuit for a radio receiver, the radio receiver including a receiver input for receiving radio frequency (RF) signals and a receiver output, the radio receiver further including a variable gain amplifier having an input coupled to the receiver input, an output and a gain control input, the variable gain amplifier amplifying the RF signals in response to a gain control signal received at the gain control input and providing amplified signals at the output of the variable gain amplifier, the radio receiver further including a filter coupled to the output of the variable gain amplifier for filtering the amplified signals and providing filtered signals to the output of the radio receiver, the automatic gain control circuit comprising:
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a signal level detector coupled to the receiver output for detecting a signal level of the filtered signals and providing a signal level signal, the signal level signal being indicative of the signal level; an amplifier circuit having an input coupled to the signal level detector and an output coupled to the gain control input, the amplifier circuit providing the gain control signal in response to the signal level signal, the amplifier circuit including a capacitor coupled to the output of the amplifier circuit; and a timer circuit providing a precharge pulse to the gain control input when the signal level signal exceeds a predetermined threshold, the precharge pulse charging the capacitor to a predetermined voltage, the predetermined voltage being applied to the gain control input to establish the gain control signal. - View Dependent Claims (12, 13, 14)
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15. A radiotelephone comprising:
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an antenna; a transmitter coupled to the antenna; a control circuit coupled to the transmitter for controlling operation of the radiotelephone; a receiver coupled to the control circuit, the receiver including; a receiver input coupled to the antenna for receiving radio frequency (RF) signals from the antenna and a receiver output coupled to the control circuit; an amplifier having an input coupled to the receiver input, an output and a gain control input; a first mixer circuit having an input coupled to the output of the amplifier and an output; a filter circuit having an input coupled to the output of the first mixer circuit and an output; a single sideband mixer having an input coupled to the output of the filter circuit and an output coupled to the receiver output; an automatic gain control circuit including; a signal level detector having an input coupled to the receiver output and an output; an integrator having an input coupled to the output of the signal level detector and an output coupled to the gain control input of the amplifier; a comparator having a first input coupled to the output of the signal level detector, a second input for receiving a reference level and an output; and a timer circuit having an input coupled to the output of the comparator and an output coupled to the gain control input, the timer circuit providing to the gain control input a voltage pulse having a predetermined time duration in response to a trigger signal received from the output of the comparator. - View Dependent Claims (16, 17)
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Specification