Radio frequency signal reception using frequency shifting by discrete-time sub-sampling down-conversion

• US 5,640,698 A
• Filed: 06/06/1995
• Issued: 06/17/1997
• Est. Priority Date: 06/06/1995
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Stanford University
• Inventors: Wooley, Bruce A., Hwang, Chien-Meen, Shen, David H., Lusignan, Bruce B.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Kincaid, Lester G.
• Application Number:
  US08/468,280
• Time in Patent Office: 742 Days
• Field of Search: 455/313, 455/323, 455/338, 455/314-316, 455/339-340, 455/307, 375/350, 375/346, 375/316, 375/340
• US Class Current: 455/323
• 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
• CPC Class Codes: H04B 1/0003 Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain digital baseband systems H04L25/00; digital modulation/demodulation H04L27/00; CDMA H04B1/707; TDMA H04B7/2643; image transmission H04N5/00
• CPC Class Codes: H04B 1/0025 using a sampling rate lower than twice the highest frequency component of the sampled signal for demodulation of angle-modulated signals H03D3/006
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16

Abstract

An RF communications receiver permits greater integration on standard silicon chips and consumes less power than previous receivers. Sub-sampling and discrete-time signal processing techniques are used to frequency down-convert, filter, amplify, and select a desired analog RF channel. A sample-and-hold circuit sub-samples the desired analog RF channel of carrier frequency f_c, thereby down-converting it to a discrete-time image signal of frequency f_i. Successive down-sampling, anti-alias filtering, and amplification of the discrete-time image signal yield a low-frequency discrete-time signal containing a down-converted channel of frequency f_k. The low-frequency discrete-time signal is then digitized, filtered, and demodulated to reveal its baseband information content.

Claims

1. A method for filtering and frequency translating an RF signal containing an RF channel of carrier frequency f_c to yield a low-frequency signal containing a down-converted channel of frequency f_k, the method comprising:

filtering the RF signal to yield a band-limited signal of bandwidth W, the band-limited signal containing a channel allocation band of bandwidth B, where the channel allocation band contains the RF channel;

discrete-time sampling the band-limited signal at a sampling frequency f_s to yield an image signal that contains an image channel of frequency f_i, where f_i <

f_s <

f_c ;

discrete-time down-converting and down-sampling the image signal using sub-sampling to yield the non-zero-frequency, low-frequency signal containing the down-converted channel of frequency f_k >

0.

2. The method of claim 1 wherein

f_i =mfk for a rational number m,

f_s -2f_i >

(W+B)/2, and

f_i =nf_s ±

f_c for an integer n which minimizes |f_i |.

3. The method of claim 1 wherein f_s /4<

f_i <

f_s /2.

4. The method of claim 3 wherein f_i =f_s /3.

5. The method of claim 1 wherein the down-converting step comprises:

discrete-time notch or bandpass filtering the image signal to prevent interfering aliasing; and

down-sampling the image signal to shift the image signal down in frequency and sample rate.

6. The method of claim 5 wherein the down-sampling step comprises successively down-sampling the image signal by factors of two.

7. The method of claim 5 wherein the discrete-time filtering step comprises amplifying the signal.

8. The method of claim 1 further comprising digitizing the low-frequency signal containing the down-converted channel.

9. A radio receiver comprising:

a receiving means for receiving an RF signal containing an RF channel of carrier frequency f_c within a channel allocation band having bandwidth B;

a filtering means for filtering the RF signal to a bandwidth W to yield a band-limited signal, the band-limited signal containing the channel allocation band;

a discrete-time sampling means for sampling the band-limited signal at a sampling frequency f_s to yield an image signal containing an image channel of frequency f_i, where f_i <

f_s <

f_c ;

a discrete-time down-converting means for down-converting and down-sampling the image signal using sub-sampling to yield a non-zero-frequency, low-frequency signal containing a down-converted channel of frequency f_k, where 0<

f_k <

f_i ;

a discrete-time channel-select filtering means for removing adjacent-channel interference from the low-frequency signal to isolate the down-converted channel; and

a demodulation means for demodulating the down-converted channel to yield a baseband signal.

10. The radio receiver of claim 9 wherein f_i =mf_k for a rational number m,

f_s -2f_i >

(W+B)/2, and

f_i =nf_s ±

f_c for an integer n which minimizes |f_i |.

11. The radio receiver of claim 9 wherein f_s /4<

f_i <

f_s /2.

12. The radio receiver of claim 11 wherein f_i =f_s /3.

13. The radio receiver of claim 9 wherein the down-converting means comprises:

a discrete-time notch or bandpass filtering means for anti-alias filtering the image signal; and

a down-sampling means for shifting the image signal down in frequency and sample rate.

14. The radio receiver of claim 13 wherein the down-sampling means comprises a 2:

1 discrete-time sampling down-converter.

15. The radio receiver of claim 13 wherein the discrete-time filtering means includes an amplifying means.

16. The radio receiver of claim 9 further comprising a digitizing means for digitizing the low-frequency signal containing the down-converted channel.

17. The radio receiver of claim 9 wherein the demodulation means comprises a demodulator chosen from the group consisting of an AM demodulator, an FM demodulator, a phase modulation demodulator, a quadrature amplitude modulation demodulator, a phase shift keying demodulator, a Gaussian minimum shift keying demodulator, and a frequency shift keying demodulator.

18. A method for filtering and frequency translating an RF signal containing an RF channel of carrier frequency f_c to yield a non-zero-frequency, low-frequency signal, the low frequency signal containing a down-converted channel of frequency f_k >

0, the method comprising;

(a) filtering the RF signal to yield a band-limited signal of bandwidth W, the band-limited signal containing a channel allocation band of bandwidth B, where the channel allocation band contains the RF channel;

(b) discrete-time sampling the band-limited signal at a sampling frequency f_s to yield an image signal that contains an image channel of frequency f_i, where f_i <

f_s <

f_c ;

(c) discrete-time filtering the image signal to remove adjacent-channel interference and unwanted aliasing interference and thereby further isolate the image channel from within the image signal to produce a discrete-time filtered image signal;

(d) discrete-time sub-sampling the discrete-time filtered image signal to simultaneously shift in frequency and reduce the sample rate of the discrete-time filtered image signal;

(e) repeating steps (c) and (d) in order to down-convert the image signal to yield the low-frequency signal containing the down-converted channel of frequency f_k >

0.

19. The method of claim 18 wherein

f_i =mf_k for a rational number m,

f_s -2f_i >

(W+B)/2, and

f_i =nf_s ±

f_c for an integer n which minimizes |f_i |.

20. The method of claim 18 wherein f_s /4<

f_i <

f_s /2.

21. The method of claim 20 wherein f_i =f_s /3.

22. The method of claim 18 wherein the sub-sampling step comprises down-sampling the image signal by a factor of two.

23. The method of claim 18 wherein the discrete-time filtering step comprises amplifying the signal.

24. The method of claim 18 further comprising digitizing the low-frequency signal.