Receiver frequency offset bias circuit for TDM radios
First Claim
1. A bias control circuit for a radio receiver used in a communication system wherein a signalling preamble is sent to said receiver prior to sending other information, said bias control circuit comprising:
- a coupling capacitor having an input terminal and an output terminal;
means for selectively coupling said capacitor input terminal to a received input signal in response to a control signal;
means for biasing said capacitor input terminal to a desired voltage in response to said control signal; and
controller means for providing said control signal in response to the reception of said signalling preamble,whereby said coupling capacitor is properly biased for the subsequent reception of said other information.
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Accused Products
Abstract
An improved bias control circuit (FIG. 2) is disclosed for a radio receiver (122) used in a communication system wherein a signalling preamble is sent prior to sending other information. The bias circuit (140) rapidly determines the DC voltage level representing the average frequency of the received signalling preamble (215), develops a DC bias voltage (275) proportional to the error in frequency between the receiver and the transmitted signal, and then selectively applies this bias voltage to the series coupling capacitor (240) located between the receiver detector (121) and the receiver processing circuitry (123). The circuit is adapted for a 0.2 GMSK receiver in a TDMA communication system, where a known 1100 bit synchronization preamble is sent in each user'"'"'s TDM time slot.
37 Citations
33 Claims
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1. A bias control circuit for a radio receiver used in a communication system wherein a signalling preamble is sent to said receiver prior to sending other information, said bias control circuit comprising:
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a coupling capacitor having an input terminal and an output terminal; means for selectively coupling said capacitor input terminal to a received input signal in response to a control signal; means for biasing said capacitor input terminal to a desired voltage in response to said control signal; and controller means for providing said control signal in response to the reception of said signalling preamble, whereby said coupling capacitor is properly biased for the subsequent reception of said other information. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A circuit for coupling an AC signal from a input node to a output node, said circuit comprising:
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a capacitor having first and second terminals; first switching means for controllably coupling said input node to said first terminal; means for determining the average DC voltage level of said AC signal at said input node; second switching means for controllably applying said average DC voltage to said first terminal; third switching means for controllably applying a reference DC voltage to said second terminal; means for coupling said second terminal to said output node; and means for controlling said first, second, and third switching means such that said average DC voltage is applied to said capacitor first terminal only during a first time period, and such that said AC signal is coupled from said input node to said output node only during a second time period not overlapping said first time period. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A method of receiving coded information in a radio receiver having a signal processor for decoding said information, said method comprising the steps of:
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(a) demodulating a modulated radio frequency (RF) carrier in a radio receiver, thereby providing a received signal; (b) determining the average DC voltage level of said received signal during a first time period; (c) determining the preferred DC reference voltage level of said signal processor for optimal information decoding; (d) precharging a capacitor to a DC precharge voltage during a second time period; (e) series coupling said received signal from said receiver to said signal processor through said precharged capacitor; and (f) decoding information from said received signal in said signal processor during a third time period, whereby said third time period does not overlap said second time period. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A radio receiver used in a communication system wherein a signalling preamble is sent prior to sending other information, said radio receiver comprising:
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receiver means for receiving a radio frequency (RF) carrier, thereby providing a received signal; signal processing means for decoding information from said received signal, said signal processing means having a preferred DC reference voltage level for optimal information decoding; capacitor means for AC coupling said received signal from said receiver means to said signal processing means; averaging means for determining the average DC voltage level of said received signal during the time period when said signalling preamble is being received; and biasing means for selectively applying a DC biasing voltage to said capacitor means in response to said averaging means at times other than when said information is being received. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33)
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Specification