Digital subharmonic sampling down-converter

• US 4,888,557 A
• Filed: 04/10/1989
• Issued: 12/19/1989
• Est. Priority Date: 04/10/1989
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: General Electric Company
• Inventors: Saulnier, Gary J., Puckette, Charles M. IV
• Primary Examiner(s): Laroche, Eugene R.
• Assistant Examiner(s): Pascal, Robert J.
• Application Number:
  US07/335,269
• Time in Patent Office: 253 Days
• Field of Search: 329/50, 329/110, 329/112, 329/122, 329/124, 455/205, 375/78
• US Class Current: 329/341
• CPC Class Codes: H03D 2200/0047 Offset of DC voltage or frequency
• CPC Class Codes: H03D 2200/005 Analog to digital conversion
• CPC Class Codes: H03D 2200/006 Signal sampling
• CPC Class Codes: H03D 2200/007 by using a logic circuit, e.g. flipflop, XOR
• CPC Class Codes: H03D 2200/008 Hilbert type transformation
• CPC Class Codes: H03D 2200/0082 Quadrature arrangements
• CPC Class Codes: H03D 3/006 by sampling the oscillations and further processing the samples, e.g. by computing techniques H03D3/007 takes precedence
• CPC Class Codes: H03D 3/008 Compensating DC offsets
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• CPC Class Codes: H03D 7/00 Transference of modulation from one carrier to another, e.g. frequency-changing H03D9/00, H03D11/00 take precedence; dielectric amplifiers, magnetic amplifiers, parametric amplifiers used as a frequency-changers H03F

Abstract

A digital subharmonic sampling converter, for use in an analog IF signal demodulator and the like, includes: an analog-to-digital converter (ADC) means receiving the IF analog signal for conversion to a digital data stream by sampling at a sampling rate frequency substantially equal to 4/(2n+1) times the IF signal frequency, where n is an integer greater than zero. A digital mixer means is used to convert the sampled data to baseband. The interleaved sequential in-phase I data words and quadrature-phase Q data words are then sorted into a pair of concurrent I and Q data word streams.

Claims

1. A digital subharmonic down-converter, receiving an analog IF signal for providing substantially simultaneous output streams of in-phase I data and quadrature-phased Q data words, comprises:

ADC means for converting the analog IF signal, having a frequency f_IF, to a stream of digital data samples taken at a sampling frequency f_c ;

digital mixer means for converting the digital data sample stream to a stream of baseband digital data words;

sorter means for separating interleaved alternating ones of the baseband data words stream into sequential sorted pairs of an in-phase I data word and a quadrature-phase Q data word; and

means for causing the ADC means sampling frequency f_c to be a subharmonic of the IF frequency, with ##EQU2## where n is a selected integer greater than zero.

2. The down-converter of claim 1, wherein the IF signal has a maximum frequency F_H and a minimum frequency F_L and n is less than K=Int(f_H /BW), where BW=(f_H -f_L).

3. The down-converter of claim 2, further comprising means for compensating the sorted pairs of data words for at least one of quadrature misalignment offset and input signal DC bias.

4. The down-converter of claim 2, wherein n=1 and ##EQU3##

5. The down-converter of claim 4, wherein f_IF is on the order of 10 MHz.

6. The down-converter of claim 5, wherein f_IF is between about 4 and about 20 MHz.

7. The down-converter of claim 2, wherein n=2 and ##EQU4##

8. The down-converter of claim 7, wherein f_IF is on the order of 10 MHz.

9. The down-converter of claim 8, wherein f_IF is between about 4 and about 20 MHz.