Sequential threshold detector

• US 4,387,465 A
• Filed: 04/13/1981
• Issued: 06/07/1983
• Est. Priority Date: 04/13/1981
• Status: Expired due to Fees

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Becker, James C.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/253,331
• Time in Patent Office: 785 Days
• Field of Search: 307/350, 307/530, 307/352, 307/353, 307/354, 307/356, 307/360, 328/135, 328/146, 328/149, 328/162, 328/150, 343/5 PN, 375/1, 375/76, 375/94, 375/96, 375/116
• US Class Current: 375/130
• CPC Class Codes: H03K 5/088 modified by switching, e.g. by a periodic signal or by a signal in synchronism with the transitions of the output signal
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold

Abstract

An improved sequential threshold detection circuit for use in the receiver of a spread-spectrum communication system is disclosed wherein the improvement resides in the employment of a feedback circuit for maintaining a pre-selected constant median dismissal time. In the preferred embodiment the feedback circuit comprises a flip-flop (70), a very long time constant integrator (72), and a one-shot (74) connected between a comparator (64) and a summing amplifier (60) for varying a threshold bias voltage applied to the summing amplifier. In an alternative embodiment, the feedback circuit serves to selectively vary the gain of a variable gain amplifier (110) in such a manner to vary the individual trial and error dismissal times to provide a substantially constant median dismissal time over the entire detection process.

The detection circuit of the invention provides a signal indicating whether the pseudo-random noise generator (26) in the system receiver (9) has been synchronized to the pseudo-random noise generator (16) in the system transmitter (8), but does so with improved reliability, accuracy and statistical performance with reduced manufacturing cost.

Claims

1. In an improved sequential threshold detection apparatus for use in the receiver of a psuedo-random noise modulation spread-spectrum system having a transmitter and a receiver including respective matched pseudo-random code generators for modulating the transmitter output signal and demodulating the receiver input signal, respectively, in accordance with identical code sequences, an integrator for integrating the input signal, a comparator for comparing the integrated input signal with a pre-selected threshold voltage such that said integrated input signal has a first relationship to said threshold voltage when said code generators are not synchronized and a second relationship to said threshold voltage when said code generators are synchronized a generator for generating a reset pulse in response to said first relationship, and a truncation timer for generating a detector output pulse in response to the existence of said second relationship for a pre-selected time duration indicating synchronization between said code generators;

the improvement comprising;

means for applying a modifying voltage to said receiver input signal so as to modify its level;

means for maintaining said modifying voltage substantially constant over an acquisition period corresponding in time to a plurality of said reset pulses; and

means for alternately increasing and decreasing said modifying voltage during successive sample periods, respectively, to provide a substantially constant median time duration between successive reset pulses over a plurality of acquisition periods.

2. The improved apparatus recited in claim 1,

said means for modifying comprising:

a differential amplifier having a positive input terminal adapted to receive said incoming signal, and having a negative terminal to which said modifying voltage is applied;

said means for maintaining comprising;

a long time constant integrator having an output terminal connected to said negative terminal, and having an input terminal; and

said means for periodically changing comprising;

a bistable multivibrator having a data terminal connected to said output terminal of said comparator and having an output terminal connected to the input terminal of said long time constant integrator; and

an astable multivibrator having a terminal for a pulse output signal of fixed time duration, said output terminal connected to the clock terminal of said bistable multivibrator, said astable multivibrator also having a trigger terminal for receiving a sample pulse during said sample period.

3. The improved apparatus recited in claim 1,

said means for modifying comprising:

a variable gain amplifier having an input terminal for receiving said incoming signal and a gain control terminal to which said modifying voltage is applied;

said means for maintaining comprising;

a long time constant integrator the output terminal of which is connected to said gain control terminal of said variable gain amplifier; and

said means for periodically changing comprising;

a bistable multivibrator having its data terminal connected to the output terminal of said comparator and its output terminal connected to the input terminal of said long time constant integrator, and an astable multivibrator having a pulse output signal of fixed time duration equal to said substantially constant median time duration, having an output terminal connected to the clock terminal of said bistable multivibrator and having a trigger terminal for receiving a sample pulse during said sample period.

4. The improved apparatus recited in claim 1,

said means for modifying comprising:

a differential amplifier having a positive input terminal to which said incoming signal is applied, and having a negative terminal to which said modifying voltage is applied;

said means for periodically changing comprising;

a variable duty cycle oscillator having a duty cycle greater than 50% for increasing said modifying voltage and a duty cycle less than 50% for decreasing said modifying voltage.

5. The improved apparatus recited in claim 1,

said means for modifying comprising:

a variable gain amplifier having an input terminal for receiving said incoming signal and a gain control terminal to which said modifying voltage is applied;

said means for periodically changing comprising;

a variable duty cycle oscillator having a duty cycle greater than 50% for increasing said modifying voltage and a duty cyle less than 50% for decreasing said modifying voltage.

6. An improved sequential threshold detection apparatus for use in a receiver of a pseudo-random noise modulation spread-spectrum system, the system of the type having matched pseudo-random code generators in transmitter and receiver, respectively, the detection apparatus for the type having means for detecting whether or not the matched code generators are synchronized;

the means for detecting comprising an integrator for receiving an incoming signal, a first comparator for ascertaining whether or not said integrated incoming signal has exceeded a first pre-selected threshold voltage indicating lack of synchronization between said code generators, a dismiss generator for generating a reset pulse when said first threshold voltage is so exceeded, and a truncation timer for generating a detector output pulse only when said threshold voltage is not so exceeded for a pre-selected time duration indicating the achievement of synchronization between said code generators;

the improvement comprising;

means for modifying the level of said incoming signal by a modifying voltage;

means for maintaining said modifying voltage substantially constant over an acquisition period corresponding to a plurality of said reset pulses; and

means for periodically changing said modifying voltage during a sample period when it is known that synchronization between said code generators cannot occur;

said changing means having a second comparator and a second pre-selected threshold voltage and means for alternately increasing and decreasing said modifying voltage during successive sample periods, respectively, and having means for controlling said increasing and decreasing to provide a substantially constant median time duration between successive reset pulses over a plurality of acquisition periods,

the output terminals of said first and second comparators connected to respective input terminals of a double pole, single throw switch for alternately connecting said first and second comparators to said dismiss generator.

7. The improved apparatus recited in claim 6,

said means for modifying comprising:

a differential amplifier having a positive input terminal to which said incoming signal is applied, and having a negative terminal to which said modifying voltage is applied;

said means for maintaining comprising;

a long time constant integrator, the output terminal of which is connected to said negative terminal of said differential amplifier; and

said means for periodically changing comprising;

a bistable multivibrator having its data terminal connected to the output terminal of said comparator and its output terminal connected to the input terminal of said long time constant integrator, and as astable multivibrator having a pulse output signal of fixed time duration equal to said substantially constant median time duration, having an output terminal connected to the clock terminal of said bistable multivibrator and having a trigger terminal for receiving a sample pulse during said sample period.

8. The improved apparatus recited in claim 6,

said means for modifying comprising:

a variable gain amplifier having an input terminal for receiving said incoming signal and a gain control terminal to which said modifying voltage is applied;

said means for maintaining comprising;

a long time constant integrator the output terminal of which is connected to said gain control terminal of said variable gain amplifier; and

said means for periodically changing comprising;

a bistable multivibrator having its data terminal connected to the output terminal of said comparator and its output terminal connected to the input terminal of said long time constant integrator, and an astable multivibrator having a pulse output signal of fixed time duration equal to said substantially constant median time duration, having an output terminal connected to the clock terminal of said bistable multivibrator and having a trigger terminal for receiving a sample pulse during said sample period.

9. The improved apparatus recited in claim 6,

said means for modifying comprising:

a differential amplifier having a positive input terminal to which said incoming signal is applied, and having a negative terminal to which said modifying voltage is applied;

said means for periodically changing comprising;

a variable duty cycle oscillator having a duty cycle greater than 50% for increasing said modifying voltage and a duty cycle less than 50% for decreasing said modifying voltage.

10. The improved apparatus recited in claim 6,

said means for modifying comprising:

a variable gain amplifier having an input terminal for receiving said incoming signal and a gain control terminal to which said modifying voltage is applied;

said means for periodically changing comprising;

a variable duty cycle oscillator having a duty cycle greater than 50% for increasing said modifying voltage and a duty cycle less than 50% for decreasing said modifying voltage.

11. In an improved sequential threshold detection appratus for use in a receiver of a pseudo-random noise modulation spread-spectrum system, said detection apparatus of the type having means for summing an incoming pseudo-random noise modulated signal and a bias voltage;

a first integrator for receiving the summed incoming signal and bias voltage;

having a comparator for receiving the output signal of said first integrator and a fixed threshold voltage and for generating at an output terminal a signal of a first level when said first integrator output signal exceeds said threshold voltage and a signal of a second level when said threshold voltage equals or exceeds said first integrator output signal;

having a generator connected to the comparator for receiving said comparator-generated signals and connected to said first integrator for resetting the first integrator upon the occurrence of said second level signal of the comparator;

having a truncation timer for generating a detector output signal only when said comparator-generated signal remains at the first level for a pre-selected period of time; and

having a bias circuit for generating said bias voltage and for adjusting said bias voltage to a level dependent upon the amplitude of said incoming signal during the occurrence of a sample pulse;

the improvement comprising;

a bistable multivibrator having an input data terminal, an output data terminal, and a clock terminal;

an astable multivibrator having a trigger terminal and an output terminal, and having a pulse duration equal to a pre-selected constant; and

a second integrator having an input terminal and an integration output terminal;

said input data terminal of said bistable multivibrator being connected to said output terminal of said second comparator,

said output data terminal of said bistable multivibrator being connected to said input terminal of said second integrator, and said clock terminal of said bistable multivibrator being connected to said output terminal of said astable multiibrator;

said trigger terminal of said astable multivibrator being connected to receive said sample pulse, and said integration output terminal of said second integrator providing said bias voltage;

whereby said bias voltage varies during each said sample pulse and said bias voltage variation causes the median time duration between said occurrences of said second level signal of said comparator to be substantially equal to said pre-selected constant pulse duration of said astable multivibrator.

12. In an improved sequential threshold detection apparatus for use in a receiver of a pseudo-random noise modulation spread-spectrum system, said detection apparatus of the type having means for summing an incoming pseudo-random noise modulated signal and a bias voltage;

a first integrator for receiving the summed incoming signal and bias voltage;

having first and second comparators for receiving said output signal of the first integrator and first and second fixed threshold voltages and for generating at an output terminal a signal of a first level when said first integrator output signal exceeds said first or second threshold voltage, respectively, and a signal of a second level when said first threshold voltage equals or exceeds said first or second integrator output signal, respectively;

having a dismiss generator to be connected to the first comparator for receiving said first comparator-generated signals and connected to said first integrator for resetting said first integrator upon the occurrence of said second level signal of said first or second comparator;

having a truncation timer for generating a detector output signal only when said first or second comparator-generated signal remains at said first level for a pre-selected period of time; and

having a bias circuit for generating said bias voltage and for adjusting said bias voltage to a level dependent upon the amplitude of the incoming signal during the occurrence of a sample pulse;

said improvement comprising;

a bistable multivibrator having an input data terminal, an output data terminal, and a clock terminal;

an astable multivibrator having a trigger terminal and an output terminal, and having a pulse duration equal to a pre-selected constant; and

a second integrator having an input terminal and an integration output terminal;

said input data terminal of said bistable multivibrator being connected to said output terminal to said second comparator,

said output data terminal of said bistable multivibrator being connected to said input terminal of said second integrator, and said clock terminal of said bistable multivibrator being connected to said output terminal of said astable multivibrator;

said trigger terminal of said astable multivibrator being connected to receive said sample pulse, and said integration output terminal of said second integrator providing said bias voltage;

the output terminals of said first and second comparators connected to respective input terminals of a double-pole, single throw switch interposed between said comparators and said dismiss generator for alternately connecting said first and second comparators to said dismiss generator,

whereby said bias voltage varies during each said sample pulse and said bias voltage variation causes said median time duration between said occurrences of said second level signal of said comparator to be substantially equal to said pre-selected constant pulse duration of said astable multivibrator.