Variable frequency rate receiver

• US 4,870,660 A
• Filed: 12/28/1987
• Issued: 09/26/1989
• Est. Priority Date: 12/28/1987
• Status: Expired due to Term

• Current Assignee: Unisys Corporation Township Line and Union Meeting Road Blue Bell PA 19424
• Original Assignee: Unisys Corporation
• Inventors: Keate, Christopher R.
• Primary Examiner(s): KUNTZ, CURTIS A
• Assistant Examiner(s): Ricci, Michael
• Application Number:
  US07/138,183
• Time in Patent Office: 638 Days
• Field of Search: 375/81, 375/88, 375/120, 375/115, 331/14, 329/50, 329/122, 329/124
• US Class Current: 375/327
• CPC Class Codes: H04L 27/2273 associated with quadrature demodulation, e.g. Costas loop

Abstract

A variable data rate receiver is provided which employs a novel phase locked loop (PLL) of the type employing a data detection loop and a tracking loop. The data detection loop is initially not coupled to the input of the voltage controlled oscillator in the tracking loop of the PLL, but is separated by an electronic switch. A phase lock detection circuit is provided which is coupled to the data detection loop and to the tracking loop for detecting the difference in the voltage error signals in the data detection loop and the tracking loop. When this error signal indicates that the tracking loop is locked on to the carrier signal the electronic switch is closed completing the phase locked loop circuit after lock on of the carrier is achieved.

Claims

1. A variable rate receiver for receiving phase shift key (PSK) data signals as an input data stream and producing drift free real time in-phase data signals at the output comprising:

a tracking loop of the type including a voltage controlled oscillator coupled to said input data stream for producing a signal at the frequency of the carrier,

a data detection loop coupled to said input data stream for producing real time data output signals,

a comparator coupled to said data detection loop for detecting data transactions,

electronic switch means coupled between said comparator and said tracking loop,

phase lock detection means coupled to said electronic switch means and to said tracking loop and to said data detection loop for detecting when the voltage error signals in said tracking loop and in said data detection loop have reached a predetermined voltage difference indicating that the tracking loop is locked on to the phase and frequency of the carrier of the input data stream, and

said phase lock detection means having means for closing said electronic switch means.

2. A variable rate receiver as set forth in claim 1 which further includes a high-speed multiplier in said phase locked loop coupled to said electronic switch.

3. A variable rate receiver as set forth in claim 1 wherein said phase locked loop comprises a high-speed multiplier coupled to the input of a loop filter, and

the output of said loop filter being coupled to the voltage controlled oscillator of said tracking loop.

4. A variable rate receiver as set forth, in claim 3 wherein said electronic switch is connected between said high-speed multiplier and said comparator.

5. A variable rate receiver as set forth in claim 1 which further includes an amplifier in said input data stream.

6. A variable rate receiver as set forth in claim 1 wherein said input data stream comprises a data free portion of carrier signal having a length in bits predetermined to be sufficient to cause said phase lock detection means to close said electronic switch means.

7. A variable rate received as set forth in claim 6 wherein said input data stream is provided with periodic data free portions of carrier signals for resynchronizing the phase of said incoming signals.

8. A variable rate receiver as set forth in claim 1 wherein said tracking loop and said data detection loop each comprise low pass filter means,

a bit synchronizer, and

means for changing the frequency of said low pass filters and for varying the frequency of said bit synchronizer in said data detection loop.

9. A variable rate receiver as set forth in claim 8 wherein said means for changing the frequency of said low pass filters comprises a processor controller coupled to programmable resistor packs in said low pass filters.

10. A variable rate receiver as set forth in claim 9 which further includes a programmable clock coupled to said processor controller.

11. A variable rate receiver as set forth in claim 1 which further includes a bit synchronizer in said data detection loop comprising an early-late gate circuit.

12. A variable rate receiver as set forth in claim 11 wherein such early-late gate circuit comprises sample and hold circuits and absolute value detectors.

13. A variable rate receiver as set forth in claim 12 which further includes a differential amplifier coupled to the output of said absolute value detectors.

14. A variable rate receiver as set forth in claim 13 which further includes delay circuit means coupled to the output of said programmable clock and to said sample and hold circuits.

15. A variable rate receiver as set forth in claim 9 wherein said programmable clock comprises a digital synthesizer clock coupled to said processor controller.

16. A method of decreasing the acquisition time in a variable data rate receiver which employs a phase lock loop circuit having a data detection loop and a tracking loop, comprising the steps of:

isolating said data detection loop from said tracking loop at the input to the tracking loop,

providing an electronic switch at the input of said tracking loop,

detecting the difference between the error voltage signal in said data detection loop and said tracking loop,

closing said electronic switch between said data detection loop and said tracking loop to reconnect as an operable circuit the phase lock loop when the error voltage signal difference indicates that the tracking loop is locked on to the carrier signal.

17. A method as set forth in claim 16 which further includes providing a burst of carrier tone signals as a preamble to the data stream input to said phase lock loop to further enhance the speed of acquisition of said carrier tone signal.