US4814719A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Unsymmetrical QPSK demodulator
Assignee: Lanteris Space LLC
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Filing: 1987-12-14
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Granted: 1989-03-21
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Expires: 2007-12-14
Abstract
Abstract The present invention is a demodulator for demodulating an unsymmetrical QPSK signal (1), i.e., one in which the amplitudes of the I and Q channels are different, and the I and Q channels have been modulated by signals having differnt bit rates. Analog versions of the I and Q modulating baseband signals are first extracted from the carrier. Each baseband signal is then subjected to a bit-rate-matched low pass filter (23, 13). The channel having the higher bit rate is subjected to a delay (32) to time-align the two baseband signals. The time-aligned filtered signals are then amplified by amplifiers (22, 12) having unequal gains that are preselected to substantially equalize the amplifier (22, 12) outputs. The amplified time-aligned filtered signals are then subjected to a phase error (E) generating means (15, 25, 16, 26, 34). The phase error (E) is passed through a loop integrator (38) and a VCO (30) and back to the baseband signal extracting means to complete a phase lock loop. Frequency searching means (40), frequency lock detect means (42, 44), and AGC control ( 46, 8) are optionally present.
Inventors
- 👤 Edward Guyer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 18:33
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/18; H04L27/22; H04L27/227; H04L27/2271; H04L27/2273; H04L27/0014; H04L2027/0044; H04L2027/0053; H04L2027/0057; H04L2027/0063; H04L2027/0067; Y; Y10; Y10S; Y10S331/00; Y10S331/02
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
169 words
A demodulator for demodulating an unsymmetrical QPSK signal having I and Q baseband analog signals modulated onto a carrier, comprising: means for extracting the I baseband analog signal and the Q baseband analog signal from the carrier; coupled to the extracting means, two bit-rate-matched low pass filters for filtering the I and Q baseband analog signals, respectively; coupled to the lowpass filter for the channel having the higher modulating bit rate, delay means for time-aligning the two filtered baseband analog signals; coupled to the time-aligned filtered baseband analog signals, an I amplifier and a Q amplifier for amplifying the two time-aligned filtered baseband analog signals, respectively, said amplifiers having different gains that are preselected to substantially equalize the amplitudes at the respective amplifier outputs; and coupled to the outputs of said two amplifiers, means for generating a phase error, said phase error being coupled to an input of a VCO in a phase lock loop arrangement; wherein said VCO has an output that is fed to the extracting means.
Claim 2
Dependent Claim
169 words
A demodulator for demodulating an unsymmetrical QPSK signal having I and Q baseband analog signals modulated onto a carrier, comprising: means for extracting the I baseband analog signal and the Q baseband analog signal from the carrier; coupled to the extracting means, two bit-rate-matched low pass filters for filtering the I and Q baseband analog signals, respectively; coupled to the lowpass filter for the channel having the higher modulating bit rate, delay means for time-aligning the two filtered baseband analog signals; coupled to the time-aligned filtered baseband analog signals, an I amplifier and a Q amplifier for amplifying the two time-aligned filtered baseband analog signals, respectively, said amplifiers having different gains that are preselected to substantially equalize the amplitudes at the respective amplifier outputs; and coupled to the outputs of said two amplifiers, means for generating a phase error, said phase error being coupled to an input of a VCO in a phase lock loop arrangement; wherein said VCO has an output that is fed to the extracting means.
Claim 3
Dependent Claim
76 words
The demodulator of claim 1 wherein: the QPSK signal comprises an I channel and a Q channel; the I channel has a higher amplitude and a higher bit rate than the Q channel; the absolute value of the amplitude of the I channel is I; the absolute value of the amplitude of the Q channel is Q; the Q channel amplifier has a gain of B; and the I channel amplifier has a gain of BQ/I.
Claim 4
Dependent Claim
125 words
The demodulator of claim 1 wherein the extracting means comprises: coupled to the QPSK signal, an in-phase power divider which produces first and second replicas of the QPSK signal; coupled to the VCO output, a quadrature power divider which outputs first and second local oscillator reference signals 90° out of phase with respect to each other; a first multiplier having as inputs the first replica and the first local oscillator reference signal, and having an output coupled to the low pass filter that operates on the I baseband analog signal; and a second multiplier having as inputs the second replica and the second local oscillator reference signal, and having an ouput coupled to the low pass filter that operates on the Q baseband analog signal.
Claim 5
Dependent Claim
99 words
The demodulator of claim 1 wherein the phase error generating means comprises: a pair of sign detectors coupled to the amplified time-aligned filtered baseband analog signals, respectively; a pair of multipliers coupled to respective outputs of the sign detectors and to opposing ones of the amplified time-aligned filtered baseband analog signals; a subtractor having as its two inputs the outputs of the two multipliers; a loop integrator having an input coupled to an output of the subtractor; and said VCO having an input coupled to an output of the loop integrator and an output coupled to the extracting means.
Claim 6
Dependent Claim
72 words
The demodulator of claim 1 further comprising: frequency searching means coupled to the phase error generating means; a lock detector coupled to the frequency searching means for deciding when the QPSK signal has been discovered; and an automatic gain controller having a first output coupled to the lock detector and a second output coupled to an amplifier inserted in the path of the QPSK signal before said signal enters the extracting means.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-03-20 | 1992-09-19 | 1993-03-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-03-20 | 1996-09-19 | 1997-03-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-03-20 | 2000-09-19 | 2001-03-21 | $7700.00 | Window Closed / Lapsed |