Time dependent, variable amplitude threshold output circuit for frequency variant and frequency invariant signal discrimination

• US 4,928,307 A
• Filed: 03/02/1989
• Issued: 05/22/1990
• Est. Priority Date: 03/02/1989
• Status: Expired due to Term

• Current Assignee: ACS Wireless Incorporated (Alaska Communications Systems Group Incorporated)
• Original Assignee: ACS Communications, Inc. (Black Box Ltd.)
• Inventors: Lynn, Dwight D.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Vaas, Randall S.
• Application Number:
  US07/318,073
• Time in Patent Office: 446 Days
• Field of Search: 381/74, 381/104, 381/106, 381/107, 381/108, 381/72, 379/395, 379/387, 379/390, 379/388, 333/14
• US Class Current: 379/395
• CPC Class Codes: H03G 7/005 using discontinuously variable devices, e.g. switch-operated
• CPC Class Codes: H04M 1/6016 in the receiver circuit

Abstract

A voice signal compression system wherein the compression threshold may be adjusted to a calibrated level. The system includes a variable gain amplifier for amplifying a voice input signal based on the application of a variable control voltage. A driver increases the power gain of the amplified input signal to provide a power-boosted output signal. In addition to applying the power-boosted output signal to an acoustic output transducer, the power-boosted output is also applied both to a peak detecting comparator and to a threshold reset timer. The comparator produces a digital output that triggers an attack/decay timing generator which produces the control voltage for the variable gain amplifier. The comparator initially is set to a high threshold state by the threshold reset timer. As the levels and peaks of the input signal increase, the comparator begins to trigger digital pulses to the attack/decay timer. At the same time, the threshold reset timer begins measuring the duration of the signal which exceeds the threshold of the comparator. If the threshold reset timer detects that the level of the power-boosted output signal exceeds the threshold of the comparator for a preselected time, then the compression threshold of the comparator is switched to a lower level. The threshold remains low until the continuous signal is removed. At this point, the circuit is reset to its normal mode of operation.

Claims

1. A signal compression system comprising:

(a) amplifier means for amplifying an input signal to provide a power-boosted output signal, the gain of the amplifier means corresponding to a variable control voltage applied to the amplifier means;

(b) means for comparing the power-boosted output signal and an initial threshold signal to provide a comparator output corresponding to the difference between the power-boosted output signal and the initial threshold signal;

(c) means responsive to the comparator output for providing a variable control voltage corresponding to the comparator output; and

(d) means responsive to the power-boosted output signal for switching the initial threshold signal to a second threshold signal if the power-boosted output signal exceeds the initial threshold signal for a pre-selected period of time.

2. A signal compression system comprising:

(a) a variable gain amplifier for amplifying an input signal to provide a power-boosted output signal, the gain of the amplifier corresponding to a control voltage applied to the amplifier;

(b) a comparator for comparing the power-boosted output signal and a first threshold level signal and for providing a digital output signal if the power-boosted output signal exceeds the first threshold level signal;

(c) timing generator means responsive to the digital output signal for generating a corresponding control voltage for the variable gain amplifier; and

(d) reset means for detecting the level of the power-boosted output signal and for switching the first threshold level signal to a second threshold level signal if the power-boosted output signal exceeds the first threshold level signal for a preselected period of time.

3. A signal compression system comprising:

(a) a variable gain amplifier for amplifying an input signal to provide an amplified input signal, the gain of the amplifier corresponding to a control voltage applied to the amplifier;

(b) a driver for increasing the power gain of the amplified input signal to provide a power-boosted output signal;

(c) a comparator for comparing the power-boosted output signal and a first threshold level signal to provide a pulsed digital output signal if the power-boosted output signal exceeds the first threshold level signal;

(d) a threshold/reset timer for detecting the level of the power-boosted output signal and for switching the first threshold level signal to a second threshold level signal if the power-boosted output signal exceeds the first threshold level signal for a preselected period of time; and

(e) an attack/decay timer responsive to the pulsed digital output signal for providing a control voltage to the variable gain amplifier that corresponds to the pulsed digital output signal.

4. A voice signal compression system as in claim 3 wherein the output signal is a differential input signal received over telephone lines.

5. A voice signal compression system comprising:

(a) a variable gain amplifier for amplifying a differential input signal received over telephone lines based on the application of a variable control voltage;

(b) a driver that increases the power gain of the amplified input signal to provide a power-boosted output signal;

(c) a peak detecting comparator that provides a pulsed output signal if the power-boosted output signal exceeds an initial compression threshold of the comparator;

(d) an attack/decay timer that generates a variable control voltage in response to the pulsed output signal; and

(e) a threshold/reset timer that switches the initial compression threshold of the comparator to a lower threshold if the power-boosted output signal exceeds the initial compression threshold for a preselected period of time.

6. A method of signal compression comprising:

(a) amplifying an input signal to provide an amplified signal corresponding to a variable gain control voltage;

(b) comparing the amplified signal to an initial threshold level signal;

(c) varying the variable gain control voltage based on the result of the comparison of the amplified signal and the initial threshold level signal;

(d) detecting the level of the amplified signal; and

(e) switching the initial threshold level signal to a second threshold level signal if the amplified signal exceeds the initial threshold level signal for a preselected period of time.