US4902979A
Expired / Lapsed
US
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Homodyne down-converter with digital Hilbert transform filtering
Assignee: General Electric Co
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Filing: 1989-03-10
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Granted: 1990-02-20
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Expires: 2009-03-10
Abstract
Abstract A homodyne down-converter, for use in an IF signal demodulator and the like, includes an analog-to-digital converter (ADC) which receives the IF analog signal for conversion to a digital data stream by sampling at a sampling rate frequency substantially equal to four times the IF signal frequency. A digital mixer controllably inverts the sampled data to convert the data to baseband, before a circuit removes the effects of DC offset in the analog IF signal applied to the ADC. A discrete Hilbert Transform filter is used for generating streams of sequential in-phase I' and quadrature-phase Q' data words, which are resampled to temporally align the two data word streams at a new data rate, thus effectively removing sample offset without the need for separate misalignment correction circuitry.
Inventors
- 👤 Charles M. Puckette, IV
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 12:05
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/007; H03D3/008; H03D2200/00; H03D2200/0041; H03D2200/0054; H03D2200/008; H03D3/006; H03D7/00
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
135 words
A homodyne down-converter, for providing substantially simultaneous output streams of in-phase I data and quadrature-phase Q data words to a digital detector means of a digital demodulator receiving an analog IF signal, comprising: ADC means for converting the analog IF signal, having a center frequency f IF , to a stream of digital data samples taken at a sampling frequency f s substantially equal to 4f IF ; digital mixer means for converting the digital data sample stream to a stream of baseband digital data words; means for removing from the data words the effect of any DC offset in the analog IF signal; and a discrete Hilbert transform filter (DHTF) means for generating streams of sequential in-phase and quadrature-phase data words, with each stream being used to form one of the down-converter output streams.
Claim 2
Dependent Claim
135 words
A homodyne down-converter, for providing substantially simultaneous output streams of in-phase I data and quadrature-phase Q data words to a digital detector means of a digital demodulator receiving an analog IF signal, comprising: ADC means for converting the analog IF signal, having a center frequency f IF , to a stream of digital data samples taken at a sampling frequency f s substantially equal to 4f IF ; digital mixer means for converting the digital data sample stream to a stream of baseband digital data words; means for removing from the data words the effect of any DC offset in the analog IF signal; and a discrete Hilbert transform filter (DHTF) means for generating streams of sequential in-phase and quadrature-phase data words, with each stream being used to form one of the down-converter output streams.
Claim 3
Dependent Claim
23 words
The down-converter of claim 1, further comprising means for resampling the pair of DHTF means output data streams at a new data rate.
Claim 4
Dependent Claim
44 words
The down-converter of claim 2, wherein the removing means comprises: means for summing the data values of each successive pair of a present data word and a next-to-last previous data word; and means for multiplying the summed data values by a factor of one-half.
Claim 5
Dependent Claim
31 words
The down-converter of claim 3, wherein the summing means includes means for delaying each of the data words by a time interval equal to the period between two successive data words.
Claim 6
Dependent Claim
32 words
The down-converter of claim 4, wherein the multiplying means include means for removing the least-significant-bit of the summed data value word and for shifting the remaining bits rightwardly by one bit position.
Claim 7
Dependent Claim
53 words
The down-converter of claim 1, wherein the DHTF means realizes the transfer function H(z)=(z+j) n /z n , where n is greater than 1; all of the real terms of said transfer function acting upon the in-phase data and all of the imaginary terms of said transfer function acting upon the quadrature-phase data.
Claim 8
Dependent Claim
96 words
The down-converter of claim 6, wherein n=2 and said DHTF means comprises: first and second means each for delaying each of a succession of input data words by a time interval substantially equal to the time interval between each pair of data samples; means for summing the data values of the input data word and the data word then at an output of the second delaying means; and means for multiplying the summed data values of a factor of one-half, to provide the in-phase data; an output of the first delaying means providing the quadrature-phase data.
Claim 9
Dependent Claim
30 words
The converter of claim 7, wherein the delay of each of said delaying means is established by an integer number of cycles of a clock signal at the sampling frequency.
Claim 10
Dependent Claim
11 words
The down-converter of claim 6, wherein n is greater than 2.
Claim 11
Dependent Claim
64 words
The converter of claim 6, wherein the data words are arranged in a serially-interleaved stream, of the form I1-Q1-I2-Q2- . . . -I i -Q i - . . . , where i is an integer, and the DHTF means provides an in-phase data word I i at a first output substantially simultaneously with a quadrature-phase data word Qi provided at a second output.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-02-19 | 1993-08-21 | 1994-02-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-02-19 | 1997-08-21 | 1998-02-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-02-19 | 2001-08-21 | 2002-02-20 | $7700.00 | Window Closed / Lapsed |