Digital receiver operating at sub-nyquist sampling rate

• US 4,893,341 A
• Filed: 08/01/1989
• Issued: 01/09/1990
• Est. Priority Date: 08/01/1989
• Status: Expired due to Term

• Current Assignee: Protocol-ip.com, LLC, Seiko Instruments Incorporated (Seiko Group)
• Original Assignee: AT&T, Inc.
• Inventors: Gehring, Mark R.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US07/388,186
• Time in Patent Office: 161 Days
• Field of Search: 329/356, 329/361, 331/20, 331/23, 331/25, 381/7, 358/144
• US Class Current: 381/7
• CPC Class Codes: H03D 1/2254 and a phase locked loop
• CPC Class Codes: H04B 1/1646 adapted for the reception of stereophonic signals

Abstract

A digital receiver samples data from an amplitude modulated subcarrier at a rate less than twice the subcarrier'"'"'s maximum frequency by sampling at known phase points. Sampling at known phase points is achieved by generating a sampling clock from a signal phase locked to and transmitted with the modulated data subcarrier.

Claims

1. A receiver for receiving an amplitude modulated subcarrier, said subcarrier being transmitted as part of an RF composite signal that includes a pilot signal, the receiver including:

a front end for converting the RF composite signal to a baseband composite signal;

a frequency source for producing a sampling clock signal;

means for phase locking said frequency source to the pilot signal in the baseband composite signal;

sampling means for sampling said composite signal at a rate determined by the sampling clock signal;

analog to digital conversion means for converting the samples produced by the sampling means into digital form;

digital filter means for digitally filtering said digitized samples to attenuate the non-subcarrier components thereof;

wherein said sampling clock signal has a frequency less than twice the maximum frequency of the modulated subcarrier.

2. The receiver of claim 1 in which the frequency source includes means for producing a sampling clock signal having a frequency that is an integral multiple of the pilot signal frequency.

3. The receiver of claim 2 in which:

the pilot signal has a frequency of 19 kilohertz;

the subcarrier signal has a carrier frequency of 66.5 kilohertz; and

the sampling clock signal has a frequency of 133 kilohertz.

4. A method of receiving data that is modulated on a subcarrier of a composite signal, the method comprising the steps:

deriving from said composite signal a reference frequency having a known relationship with the subcarrier frequency;

sampling the composite signal periodically at certain phase conditions of the reference frequency;

digitizing the sampled composite signal to yield digital data; and

filtering said digital data to attenuate the non-subcarrier components of the digitized composite signal;

wherein said sampling occurs at a frequency twice the subcarrier frequency.