Echo suppressor

Claim 2

An echo suppressor for reducing echo signals in telephone systems of the type that include separate transmit and receive signal channels, said echo suppressor comprising the combination of a first relatively high loss attenuation pad for said transmit channel, a threshold detecting means coupled to said receive channel for linearly comparing the receive channel signal level with a predetermined threshold level, and a first switching means coupled between said threshold detecting means and said first attenuation pad for inserting and removing said first attenuation pad into and out of said transmit channel as said receive channel signal level rises above and drops below, respectively, said threshold level.

Claim 3

The echo suppressor of claim 1 further including a first delay means coupled between said threshold detecting means and said first switching means for delaying the removal of said first attenuation pad from said transmit channel for a predetermined period after said receive channel signal level drops below said threshold level.

Claim 4

The echo suppressor of claim 2 wherein said first attenuation pad comprises first and second electronic devices coupled in series and shunt, respectively, with said transmit channel, and said first switching means inserts said attenuation pad into said transmit channel by switching said first electronic device to a nonconductive state and said second electronic device to a conductive state and removes said first attenuation pad from said transmit channel by switching said first electronic device to a conductive state and said second electronic device to a nonconductive state, whereby said first attenuation pad is inserted and removed from said transmit channel without the production of switching transients.

Claim 5

The echo suppressor of claim 3 wherein said first electronic device is a first transistor having a collector-emitter circuit connected in series with said transmit channel and a base coupled to said first switching means, and said second electronic device is a second transistor having a collector-emitter circuit connected in shunt with said transmit channel and a base coupled to said first switching means, said first and second transistors being rapidly switched by said first switching means between nonconductive states and states of saturated conduction, whereby the attenuation provided by said first and second transistors to signals in said transmit channel abruptly changes between a very low negligible level and a much higher level as said first attenuation pad is inserted into and removed from said transmit channel.

Claim 6

The echo suppressor of claim 2 further including a peak detector means coupled to said receive channel for providing a floating reference signal with a level that is linearly related to an average peak level of the receive channel signal, a comparator means coupled to said peak detector and said transmit channel for linearly comparing the transmit channel peak signal level with the level of said floating reference signal, an inhibiting means coupled to said first switching means, and a second switching means coupled between said comparator means and said inhibiting means for activating and deactivating said inhibiting means in response to said transmit channel peak signal level rising above and dropping below, respectively, the level of said floating reference signal, said inhibiting means being effective when activated to cause said first switching means to remove said first attenuation pad from said transmit channel and to prevent said first swiTching means for reinserting said first attenuation pad into said transmit channel.

Claim 7

The echo suppressor of claim 5 further including a second relatively low loss attenuation pad for said receive channel, said second switching means being coupled to said second attenuation pad for inserting and removing said second attenuation pad into and out of said receive channel as said transmit channel peak signal level rises above and drops below, respectively, the level of said floating reference signal.

Claim 8

The echo suppressor of claim 6 further including a second delay means coupled between said comparator means and said second switching means for delaying the deactivation of said inhibiting means and the removal of said second attenuation pad from said receive channel for a predetermined period after the transmit channel peak signal level drops below the level of said floating reference signal.

Claim 9

The echo suppressor of claim 7 wherein said second attenuation pad comprises at least one unidirectional conducting device coupled in shunt with said receive channel, and said second switching means inserts and removes said second attenuation pad into and out of said receive channel by forward biasing and reverse biasing, respectively, said unidirectional conducting device.

Claim 10

The echo suppressor of claim 7 wherein said second switching means gradually inserts and removes the loss provided by said second attenuation pad into and out of said receive channel whereby changes in the receive channel signal level caused by the insertion and removal of said second attenuation pad are gradual.

Claim 11

The echo suppressor of claim 9 wherein said receive channel is a balanced channel, said second attenuation pad comprises a pair of identically poled diodes each connected between a respective side of said receive channel and said second switching means, and said second switching means applies a gradually increasing and a gradually decreasing forward bias to said diodes as said second attenuation pad is inserted and removed, respectively, from said receive channel to thereby gradually vary the attenuation afforded by said diodes.

Claim 12

In an echo suppressor for telephone systems having separate transmit and receive signal channels, the combination comprising a first attenuation pad including a first transistor having a collector-emitter circuit connected in series with said transmit channel and a base, and a second transistor having a collector-emitter circuit connected in shunt across said transmit channel and a base; and a control circuit coupled between said receive channel and the bases of said first and second transistors for switching said first transistor between a nonconductive state and a state of saturated conduction and said second transistor between a state of saturated conduction and a nonconductive state as said receive channel signal rises above and drops below, respectively, a predetermined threshold level to thereby sharply increase and reduce the attenuation in said transmit channel.

Claim 13

In an echo suppressor for telephone systems having separate transmit and receive signal channels, the combination comprising a first attenuation pad including a first transistor having a collector-emitter circuit connected in series with said transmit channel and a base, and a second transistor having a collector-emitter circuit connected in shunt across said transmit channel and a base; and a control circuit coupled between said receive channel and the bases of said first and second transistors for switching said first transistor between a nonconductive state and a state of saturated conduction and said second transistor between a state of saturated conduction and a nonconductive state as said receive channel signal rises above and drops below, respectively, a predetermined threshold level to thereby sharply increase and reduce the attenuation in said transmit channel.

Claim 14

The combination of claim 11 wherein said control circuit is also coupled to said transmit channel, and further including a pair of identically poled diodes each connected between a respective side of said receive channel and said control circuit, said control circuit forward biasing and reverse biasing said diodes as said transmit channel signal rises above and drops below, respectively, an average peak level of said receive channel signal.

Claim 15

In an echo suppressor for telephone systems having separate transmit and receive signal channels, the combination comprising a peak detector means coupled to said receive channel for providing a floating reference signal that has a level which is representative of the average peak level of the receive channel signal, a comparator means coupled to said peak detector means and to said transmit channel for comparing the transmit channel signal level with the level of said floating reference signal, a switching means coupled to said comparator to be gradually switched to one state of conduction and to another state of conduction as said transmit channel signal level rises above and drops below, respectively, the level of said floating reference signal, and an attenuation pad connected in said receive channel and coupled to said switching means, said attenuation pad providing a gradually increasing amount of attenuation as said switching means is switched to said one state of conduction and a gradually decreasing amount of attenuation as said switching means is switched to said other state of conduction.

Claim 16

In an echo suppressor for telephone systems having separate transmit and receive signal channels, the combination comprising a peak detector means coupled to said receive channel for providing a floating reference signal that has a level which is representative of the average peak level of the receive channel signal, a comparator means coupled to said peak detector means and to said transmit channel for comparing the transmit channel signal level with the level of said floating reference signal, a switching means coupled to said comparator to be gradually switched to one state of conduction and to another state of conduction as said transmit channel signal level rises above and drops below, respectively, the level of said floating reference signal, and an attenuation pad connected in said receive channel and coupled to said switching means, said attenuation pad providing a gradually increasing amount of attenuation as said switching means is switched to said one state of conduction and a gradually decreasing amount of attenuation as said switching means is switched to said other state of conduction.

Claim 17

The combination of claim 13 wherein said attenuation pad comprises a pair of identically poled, normally back biased, semiconductor diodes each connected between a respective side of said receive channel and said switching means, and wherein said switching means applies a gradually increasing and a gradually decreasing forward bias to said diodes as said switching means is gradually switched to said one state of conduction and to said other state of conduction, respectively.

Claim 18

The combination of claim 13 further including inhibiting means coupled to said switching means, and means to manually activate said inhibiting means for switching said switching means to said other state of conduction and for maintaining said switching means in said other state of conduction regardless of the relative levels of said transmit channel signal and said floating reference signal.

Claim 19

For long distance telephone systems of the type that include a 4-wire circuit which provides separate transmit and receive channels for both a near end subscriber and a far end subscriber, a differential split echo suppressor for inserting and removing loss into and out of the transmit and receive channels for the near end subscriber to prevent the return of potentially disturbing echo signals toward the far end subscriber while permitting the near end subscriber to break-in at will, said echo suppressor comprising the combination of a first attenuation pad for providing a relatively large amount of suppression loss, a second attenuation pad for providing a relatively small amount of break-in loss, a full wave rectifying means for providing a DC signal that has a level which is linearly related to and which closely follows changes in the near end receive channel level, a threshold detecting means coupled to said full wave rectifying means for comparing the level of said DC signal with a predetermined threshold level, a first switching means coupled between said threshold detecting means and said first attenuation pad for inserting and removing said first attenuation pad into and out of said near end transmit channel as the level of said DC signal rises above and drops below, respectively, said threshold level, a first delay means coupled to said switching means for delaying the removal of said first attenuation pad from said near end transmit channel in response to a drop of said DC signal to a level below said threshold level until the level of said DC signal has remained below said threshold level for a predetermined suppression hangover time, an inhibiting means coupled to said first switching means, said inhibiting means being effective when activated to cause said first switching means to remove said first attenuation pad from said near end transmit channel and to maintain said first attenuation pad removed from said near end transmit channel until said inhibiting means is deactivated, a peak detector means coupled to said full wave rectifying means for providing a floating reference signal that has a level that is linearly related to the average peak level of said near end receive channel signal, a comparator means for comparing the near end transmit channel signal level with the level of said floating reference signal, a second switching means coupled between said comparator and both said inhibiting means and said second attenuation pad for activating and deactivating said inhibiting means and inserting and removing saiD second attenuation pad into and out of said receive channel as said near end transmit channel signal level rises above and drops below, respectively, the level of said floating reference signal, and a second delay means coupled to said second switching means for delaying the deactivation of said inhibiting means and the removal of said second attenuation pad from said near end receive channel until said near end transmit channel signal level has remained below the level of said floating reference signal for a predetermined break-in hangover time.

Claim 20

For long distance telephone systems of the type that include a 4-wire circuit which provides separate transmit and receive channels for both a near end subscriber and a far end subscriber, a differential split echo suppressor for inserting and removing loss into and out of the transmit and receive channels for the near end subscriber to prevent the return of potentially disturbing echo signals toward the far end subscriber while permitting the near end subscriber to break-in at will, said echo suppressor comprising the combination of a first attenuation pad for providing a relatively large amount of suppression loss, a second attenuation pad for providing a relatively small amount of break-in loss, a full wave rectifying means for providing a DC signal that has a level which is linearly related to and which closely follows changes in the near end receive channel level, a threshold detecting means coupled to said full wave rectifying means for comparing the level of said DC signal with a predetermined threshold level, a first switching means coupled between said threshold detecting means and said first attenuation pad for inserting and removing said first attenuation pad into and out of said near end transmit channel as the level of said DC signal rises above and drops below, respectively, said threshold level, a first delay means coupled to said switching means for delaying the removal of said first attenuation pad from said near end transmit channel in response to a drop of said DC signal to a level below said threshold level until the level of said DC signal has remained below said threshold level for a predetermined suppression hangover time, an inhibiting means coupled to said first switching means, said inhibiting means being effective when activated to cause said first switching means to remove said first attenuation pad from said near end transmit channel and to maintain said first attenuation pad removed from said near end transmit channel until said inhibiting means is deactivated, a peak detector means coupled to said full wave rectifying means for providing a floating reference signal that has a level that is linearly related to the average peak level of said near end receive channel signal, a comparator means for comparing the near end transmit channel signal level with the level of said floating reference signal, a second switching means coupled between said comparator and both said inhibiting means and said second attenuation pad for activating and deactivating said inhibiting means and inserting and removing saiD second attenuation pad into and out of said receive channel as said near end transmit channel signal level rises above and drops below, respectively, the level of said floating reference signal, and a second delay means coupled to said second switching means for delaying the deactivation of said inhibiting means and the removal of said second attenuation pad from said near end receive channel until said near end transmit channel signal level has remained below the level of said floating reference signal for a predetermined break-in hangover time.

Claim 21

The differential split echo suppressor of claim 16 wherein said full wave rectifying means comprises an operational amplifier having an inverting input coupled to said receive channel and an output, a pair of oppositely poled diodes connected in parallel through respective feedback resistors between the output and the inverting input of said operational amplifier, and a summing circuit having one input coupled to said receive channel and another input coupled to a junction between one of said diodes and its respective feedback resistor.

Claim 22

The differential split echo suppressor of claim 16 wherein said first attenuation pad comprises a first transistor having a collector-emitter circuit connected in series with said near end transmit channel and a base coupled to said first switching means, and a second transistor having a collector-emitter circuit connected in shunt across said near end transmit channel and a base coupled to said first switching means, and wherein said first switching means inserts said first attenuation pad into said transmit channel by switching said first transistor to a nonconductive state and said second transistor to a state of saturated conduction and removes said first attenuation pad from said near end transmit channel by switching said first transistor to a state of saturated conduction and said second transistor to a nonconductive state, whereby said first attenuation pad is inserted and removed from said near end transmit channel without the production of switching transients.

Claim 23

The differential split echo suppressor of claim 16 wherein said second attenuation pad comprises a pair of identically poled, normally back biased, semiconductor diodes each connected between a respective side of said near end receive channel and said second switching means, and said second switching means applies a gradually increasing and a gradually decreasing forward bias to said diodes for respectively inserting and removing said second attenuation pad into and from said near end receive channel, whereby said second attenuation pad is inserted and removed from said near end receive channel without the production of switching transients and while causing only gradual changes in the near end receive channel signal level.

Claim 24

The differential split echo suppressor of claim 19 wherein said first attenuation pad comprises a first transistor having a collector-emitter circuit connected in series with said near end transmit channel and a base coupled to said first switching means, and a second transistor having a collector-emitter circuit connected in shunt across said near end transmit channel and a base coupled to said first switching means, and wherein said first switching means inserts said first attenuation pad into said transmit channel by switching said first transistor to a nonconductive state and said second transistor to a state of saturated conduction and removes said first attenuation pad from said near end transmit channel by switching said first transistor to a state of saturated conduction and said second transistor to a nonconductive state, whereby said first attenuation pad is inserted and removed from said near end transmit channel without the production of switching transients.

Claim 25

The differential split echo suppressor of claim 20 wherein said full wave rectifying means comprises an operational amplifier having an inverting input coupled to said receive channel and an output, a pair of oPpositely poled diodes connected in parallel through respective feedback resistors between the output and the inverting input of said operational amplifier, and a summing circuit having one input coupled to said receive channel and another input coupled to a junction between one of said diodes and its respective feedback resistor.

Claim 28

The method of claim 22 further including the steps of deriving from said DC signal a floating reference signal that has a level which is linearly related to the near end receive channel average peak signal level, comparing the near end transmit channel signal level with the level of said floating reference signal, inserting and removing a second attenuation pad into and from said near end receive channel as said near end transmit channel signal level rises above and drops below, respectively, the level of said floating reference signal, inhibiting and enabling the insertion of said first attenuation pad into said near end transmit channel as said transmit channel signal level rises above and drops below, respectively, the level of said floating reference signal, and delaying the removal of said second attenuation pad from said near end receive channel and preventing the insertion of said first attenuation pad into said near end transmit channel until the transmit channel signal level has remained below the level of said floating reference signal for a predetermined time.