Digital FM discriminator

• US 3,909,599 A
• Filed: 11/23/1973
• Issued: 09/30/1975
• Est. Priority Date: 11/23/1973
• Status: Expired due to Term

• Current Assignee: Robert F. Brown Jr, Wayne B. Trott Jr
• Original Assignee: Robert F. Brown Jr, Wayne B. Trott Jr
• Inventors: Trott, Wayne B. Jr., Brown, Robert F. Jr.
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Smith, Jerry
• Application Number:
  US05/418,233
• Time in Patent Office: 676 Days
• Field of Search: 235/150.3,151.3 325/349 324/78D,79D 328/140 329/104,126,129,140
• US Class Current: 702/78
• CPC Class Codes: G01F 15/024 involving digital counting
• CPC Class Codes: G01P 5/14 by measuring differences of pressure in the fluid
• CPC Class Codes: G01R 23/02 Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
• CPC Class Codes: H03D 3/04 by counting or integrating cycles of oscillations arrangements for measuring frequencies G01R23/10

Abstract

A discriminator for converting a frequency modulated signal into a digital representation whose magnitude changes with the frequency of the signal, wherein the FM signal is periodically sampled and converted with an accuracy of resolution that exceeds the resolution obtainable merely by counting FM cycles for a fixed time interval, first by varying the boundaries of the counting interval window sufficiently that it always begins and ends at a predetermined point on the FM waveform so that an integral number of cycle are counted, and second by using several identical sets of counters operating during different series of counting window cycles that are mutually staggered and overlapping in real time thereby to permit each counting window to be longer in real time than the intervals between which the output counts of the discriminator are to be sampled.

Claims

1. A discriminator system for converting a frequency modulated (FM) signal whose frequency represents recoverable intelligence into a magnitude representation whose resolution exceeds the resolution obtainable merely by counting cycles of the FM signal over a fixed time interval, comprising:

a. means for receiving said FM signal and delivering data pulses representing its cycles;

b. a source of clock pulses delivering pulses at higher frequency than said FM signal;

c. data counter means operative when actuated to count said data pulses;

d. clock counter means operative when actuated to count said clock pulses, and having decoder means operative to deliver a STOP signal when the clock counter means has counted a certain number of said clock pulses representing a counting window of fixed duration;

e. control circuitry establishing repeating data acquisition cycles each including one of said windows, the control circuitry being operative upon occurrence of a data pulse at the beginning of a cycle to enable both counter means to commence a counting window, and the control circuitry being operative upon the occurrence of said STOP signal to await the occurrence of the next data pulse and thereupon to terminate the counting of both counter means; and

f. calculator means responsive to the number of data pulses counted and to the number of clock pulses counted in the same cycle to calculate said converted representation whose magnitude is proportional to the number of data pulses counted but corrected by a factor relating the number of clock pulses counted within the window and the number of clock pulses incrementally counted between the occurrence of the STOP signal and the subsequent occurrence of the next data pulse, said calculator means including means operative after each counting cycle to calculate said representation by multiplying a constant times the count in the data counter means scaled by said factor which comprises the ratio of the count in the clock pulse counter means upon the occurrence of the STOP signal divided by the latter count plus the clock pulse count incrementally counted between the occurrence of the STOP signal and the subsequent occurrence of said next data pulse.

2. The system as set forth in claim 1, wherein said control circuitry includes logic means operative after said termination of the counting to load the counts from said counter means into said calculator means and to reset said counter means.

3. The system as set forth in claim 1, including means controlling the applying of data pulses to the data counter means and further including gate means controlling the applying of clock pulses to the clock counter means, and said control circuitry controlling the actuation and termination of counting in said counter means by controlling said gate means.

4. The system as set forth in claim 1, wherein for the purpose of further improving the resolution of said conversion of the FM signal to a magnitude representation the pulses are counted in real time acquisition cycles which are longer than the time intervals between calculations by said calculator means, said system further comprising means in the control circuitry for establishing multiple separate series of repeating data acquisition cycles which series are staggered in real time and mutually overlap, and said counter means including for each of said separate series of cycles paired data and clock counters;

and said system including output control logic for sequentially coupling said paired counters for each terminating acquisition cycle to said calculator means.

5. The system as set forth in claim 4, wherein the calculator means has means to deliver an interrogation command at the beginning of each of its calculation intervals, and said control circuitry comprising separate output control logic for each set of counters and separate counter control logic for each set of counters, and the control circuitry including means to select a different set of counters and control logic in response to each successive interrogation command, the selected output control logic being operative to load the counts of its paired counters into the calculator means and reset the counters, and the selected counter control logic being operative to actuate the reset counters to commence counting again.