Squelch circuit having short and long time constant filters for squelch tail elimination

Claim 2

A squelch filter circuit for coupling a detected noise voltage to a switch for actuating the same, said squelch filter circuit including in combination: first circuit means with filter means having a particular time constant, said first circuit means being adapted to receive the detected noise voltage and being responsive thereto to develop a first filtered noise voltage; second circuit means having a time constant greater than said particular time constant, said second circuit means being adapted to be interrupted and further adapted to develop a second voltage in response to the detected noise voltage; a switch responsive to said first and second voltages greater than a predetermined magnitude to be actuated thereby; circuit means coupling said first and second circuit means to the switch; signal level detector means for developing a control signal in response to the detected noise voltage being greater than a particular magnitude; and means responsive to said control signal for interrupting the second circuit means to remove said second voltage from the switch.

Claim 3

A squelch filter circuit for coupling a detected noise voltage to a switch for actuating the same, said squelch filter circuit including in combination, first filter means having a particular time constant, said first filter means being adapted to receive the detected noise voltage and being responsive thereto to develop a first filtered noise voltage, second filter means having a time constant greater than said particular time constant, said second filter means being adapted to be interrupted and further adapted to receive the detected noise voltage and to develop a second filtered noise voltage therefrom, the switch being responsive to the larger of said first and second filtered noise voltages greater than a predetermined magnitude to be actuated thereby, circuit means coupling said first and second filter means to the switch, signal level detector means to develop a control signal in response to the detected noise voltage being greater than a particular magnitude, and means responsive to said control signal for interrupting the second filter means to remove said second filtered noise voltage from the switch.

Claim 4

A squelch filter circuit for coupling a detected noise voltage to a switch for actuating the same, said squelch filter circuit including in combination, first filter means having a particular time constant, said first filter means being adapted to receive the detected noise voltage and being responsive thereto to develop a first filtered noise voltage, second filter means having a time constant greater than said particular time constant, said second filter means being adapted to be interrupted and further adapted to receive the detected noise voltage and to develop a second filtered noise voltage therefrom, the switch being responsive to the larger of said first and second filtered noise voltages greater than a predetermined magnitude to be actuated thereby, circuit means coupling said first and second filter means to the switch, signal level detector means to develop a control signal in response to the detected noise voltage being greater than a particular magnitude, and means responsive to said control signal for interrupting the second filter means to remove said second filtered noise voltage from the switch.

Claim 5

The squelch filter circuit of claim 2 wherein, said second filter means includes charge storing means and first and second charging path means connected to said charge storing means, said first charging path being adapted to receive said detected noise voltage and couple the same to said charge storage means, said second charging path means having at least a portion thereof different from said first charging path means and further having a higher impedance than said first charging path means whereby the time constant of said charge storing means and said second charging path means is greater than said particular time constant.

Claim 6

The squelch filter circuit of claim 3 wherein, said first charging path means includes amPlifier means having an input circuit adapted to receive the detected noise signal, said amplifier means further having a low impedance output circuit coupled to said charge storing means to provide a charging path for the rapid supply of charges to said charge storing means.

Claim 7

The squelch filter circuit of claim 3 wherein, said circuit means includes gate means coupling said second filter means to the switch, said gate means acting to prevent the coupling of said first filtered noise voltage to the second filter means when said first filtered noise voltage exceeds the second filtered noise voltage.

Claim 8

The squelch filter circuit of claim 5 wherein, said circuit means further includes a voltage divider circuit coupled to said first filter means for reducing the amplitude of said first filtered noise voltage.

Claim 9

A squelch filter circuit for coupling a detected noise voltage to an audio switch for actuating the same, said squelch filter circuit including in combination, first filter means having a particular time constant and being adapted to receive the detected noise voltage, said first filter means further being responsive to the detected noise voltage to develop a first filtered noise voltage and being coupled to the audio switch for applying said first filtered noise voltage thereto, second filter means including charge storage means and a first charging path having a time constant greater than said particular time constant, said second filter means further including a second charging path cooperating with said charge storage means and having a time constant less than the time constant provided by said first charging path and said charge storage means, said second charging path being adapted to be interrupted in response to a control signal applied thereto and further being adapted to receive the detected noise voltage, said second filter means being responsive to the detected noise voltage to develop a second filtered noise voltage, gate means coupling said second filter means to the audio switch and said first filter means, said gate means being responsive to the magnitude of said first and second filtered noise voltages to apply said second filtered noise voltage to the audio switch with said first filtered noise voltage less than the second filtered noise voltage and further to block said first filtered noise voltage from said second filter means with said first filtered noise voltage greater than said second filtered noise voltage, signal level detector means coupled to said first filter means for receiving said first filtered noise voltage and further being coupled to said second charging path, said signal level detector means being responsive to said first filtered noise voltage greater than a predetermined level to develop said control signal whereby said second filtered noise voltage is interrupted.

Claim 10

A squelch filter circuit for coupling a detected noise voltage to an audio switch for actuating the same, said squelch filter circuit including in combination, first filter means having a particular time constant and being adapted to receive the detected noise voltage, said first filter means further being responsive to the detected noise voltage to develop a first filtered noise voltage and being coupled to the audio switch for applying said first filtered noise voltage thereto, second filter means including charge storage means and a first charging path having a time constant greater than said particular time constant, said second filter means further including a second charging path cooperating with said charge storage means and having a time constant less than the time constant provided by said first charging path and said charge storage means, said second charging path being adapted to be interrupted in response to a control signal applied thereto and further being adapted to receive the detected noise voltage, said second filter means being responsive to the detected noise voltage to develop a second filtered noise voltage, gate means coupling said second filter means to the audio switch and said first filter means, said gate means being responsive to the magnitude of said first and second filtered noise voltages to apply said second filtered noise voltage to the audio switch with said first filtered noise voltage less than the second filtered noise voltage and further to block said first filtered noise voltage from said second filter means with said first filtered noise voltage greater than said second filtered noise voltage, signal level detector means coupled to said first filter means for receiving said first filtered noise voltage and further being coupled to said second charging path, said signal level detector means being responsive to said first filtered noise voltage greater than a predetermined level to develop said control signal whereby said second filtered noise voltage is interrupted.

Claim 11

The squelch filter circuit of claim 7 wherein, said second charging path includes an emitter follower circuit having an input circuit and an output circuit, said output circuit being coupled to said charge storage means, said signal level detector means including bias circuit means coupled to said input circuit means, said bias circuit means being responsive to said control signal to bias off said emitter follower circuit.

Claim 12

The squelch filter circuit of claim 8 wherein, said gate means includes a diode poled to conduct with said second filtered noise voltage greater than said first filtered noise voltage.

Claim 13

The squelch filter circuit of claim 9 wherein, said charge storage means is a capacitor.

Claim 14

A squelch circuit for a receiver which has an output circuit for translating detected signals, such squelch circuit selectively enabling and disabling the output circuit in response to a detected noise voltage which varies with the level of a received signal, and acting to disable the output circuit following termination of the received signal with a time delay which depends upon the received signal level, said squelch circuit including in combination: first circuit means including filter means having a particular time constant, said first circuit means being adapted to receive the detected noise voltage and being responsive thereto to develop a first filtered noise voltage, said particular time constant defining the minimum delay in disabling the audio circuit; second circuit means coupled to said first circuit means and including filter means having a time constant greater than said particular time constant, said second circuit means being responsive to said first filtered noise voltage to develop a second voltage and being adapted to receive a control signal; switch means coupled to the output circuit of the receiver for controlling the same and responsive to said second voltage to be actuated thereby; signal level detector means for developing a control signal which changes in response to the detected noise voltage; and means for applying said control signal to said second circuit means for modifying the action of second circuit means in accordance with the level of the detected noise voltage.

Claim 15

A squelch circuit for a receiver which has an output circuit for translating detected signals, such squelch circuit selectively enabling and disabling the output circuit in response to a detected noise voltage which varies with the level of a received signal, and acting to disable the output circuit following termination of the received signal with a time delay which depends upon the received signal level, said squelch circuit including in combination: first circuit means including filter means having a particular time constant, said first circuit means being adapted to receive the detected noise voltage and being responsive thereto to develop a first filtered noise voltage, said particular time constant defining the minimum delay in disabling the audio circuit; second circuit means coupled to said first circuit means and including filter means having a time constant greater than said particular time constant, said second circuit means being responsive to said first filtered noise voltage to develop a second voltage and being adapted to receive a control signal; switch means coupled to the output circuit of the receiver for controlling the same and responsive to said second voltage to be actuated thereby; signal level detector means for developing a control signal which changes in response to the detected noise voltage; and means for applying said control signal to said second circuit means for modifying the action of second circuit means in accordance with the level of the detected noise voltage.

Claim 16

A squelch circuit in accordance with claim 11 wherein said signal level detector means includes resistor means and a transistor connected in series therewith, with said transistor being selectively rendered conductive in accordance with the level of the detected noise voltage to complete the circuit through said resistor means.