Automatic gain control system for a direct conversion receiver
First Claim
1. An automatic gain control system for use in a direct conversion receiver having a plurality of baseband signal channels for carrying separate baseband signal components, comprising:
- a polyphase rectifier for generating a rectified signal reflective of the voltage levels on all of said channels;
control means coupled to said rectifier for generating a digital word control signal corresponding to the voltage level of said rectified signal and suitable for use in controlling a multiplying DAC;
a plurality of multiplying DACs which are coupled to said control means and one of which is installed on each of said channels for uniformly attenuating said baseband signal components to varying degrees in response to said digital word control signal; and
clock generator means for supplying clock signals at different frequencies to said control means in order to select the speed of operation of said gain control system and provide for rapidly increasing attenuation (fast attack) and slowly decreasing attenuation (slow release) when the receiver is processing amplitude modulated signals and provide for both very rapidly increasing and very rapidly decreasing attenuation when the receiver is processing angle modulated signals.
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Abstract
A direct conversion receiver having a tri-phase architecture including three separate baseband signal channels. RF communications signals which are being tuned by the receiver are split into three equal and in-phase components which are mixed with three equal but substantially out-of phase injection signals on frequency with the communications signal. The resulting baseband component signals are independently filtered and amplified on the three signal channels. The baseband components are then directed to a signal processing unit which corrects the baseband components for gain or phase mismatch errors between the signal channels based on the information carried by the three components and thereafter demodulates the signals in order to acquire the information carried by the RF communications signal. An automatic gain control system and a signal filtering system adapted for use with direct conversion receivers are also disclosed.
144 Citations
4 Claims
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1. An automatic gain control system for use in a direct conversion receiver having a plurality of baseband signal channels for carrying separate baseband signal components, comprising:
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a polyphase rectifier for generating a rectified signal reflective of the voltage levels on all of said channels; control means coupled to said rectifier for generating a digital word control signal corresponding to the voltage level of said rectified signal and suitable for use in controlling a multiplying DAC; a plurality of multiplying DACs which are coupled to said control means and one of which is installed on each of said channels for uniformly attenuating said baseband signal components to varying degrees in response to said digital word control signal; and clock generator means for supplying clock signals at different frequencies to said control means in order to select the speed of operation of said gain control system and provide for rapidly increasing attenuation (fast attack) and slowly decreasing attenuation (slow release) when the receiver is processing amplitude modulated signals and provide for both very rapidly increasing and very rapidly decreasing attenuation when the receiver is processing angle modulated signals. - View Dependent Claims (2, 3, 4)
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Specification