Transceiver circuit and method

Abstract

A modem transceiver circuit and method is disclosed, the transceiver circuit having a line drive transformer, a transmit circuit and a receive circuit. The receive circuit features a receive operational amplifier which is enabled when the voltage magnitude of a data signal received by the modem transceiver circuit is below a predetermined threshold. The receive operational amplifier is disabled when the voltage magnitude of the data signal is greater than or equal to the predetermined threshold. When enabled, the receive operational amplifier amplifies the data signal for further processing by other modem circuitry. When disabled, a series resistance comprising an input resistance and a feedback resistance attenuates the data signal for further processing by other modem circuitry.

Having thus described the invention, it is claimed:  
     
         1 . A transceiver circuit for a modem, comprising: 
 a line driver transformer;    a transmission circuit coupled to the line driver transformer;    a receive circuit coupled to the line driver transformer, the receive circuit including: 
 an amplified signal pathway defined by a summing circuit having a receive operational amplifier coupled to both a first input resistance and a feedback resistance when the receive operational amplifier is in an active state;  
 an attenuated signal pathway defined by the first input resistance in series with the feedback resistance when the receive operational amplifier is in an inactive state, the attenuated signal pathway attenuating a data signal input; and  
 a modem circuit responsive to a magnitude of a received signal to select between the amplified signal pathway and the attenuated signal pathway.  
   
     
     
         2 . The transceiver circuit of  claim 1 , wherein the summing circuit further comprises: 
 the input resistance coupling the line drive transformer to a signal input on the receive operational amplifier; and    the feedback resistance coupling the signal input to a signal output of the receive operational amplifier.    
     
     
         3 . The transceiver circuit of  claim 1 , wherein the receive circuit further comprises a transmission signal subtraction circuit coupling the transmit circuit to a second input resistance of the summing circuit.  
     
     
         4 . The transceiver circuit of  claim 1 , further comprising measuring means for determining whether the voltage of an input signal received by the transceiver circuit is greater than a predetermined threshold.  
     
     
         5 . The transceiver circuit of  claim 4 , further comprising means for triggering the enable/disable input responsive to the measuring means.  
     
     
         6 . The transceiver circuit of  claim 5 , wherein the means for triggering the enable/disable input is a switch.  
     
     
         7 . A transceiver circuit in a modem, comprising: 
 a transformer means for interfacing the transceiver circuit with a local loop;    a transmission means for transmitting an upstream data signal, the transmission means being coupled to the transformer means;    a receive means for receiving an downstream data signal, the receive means being coupled to the transformer means, the receive means including: 
 an amplification means for amplifying the downstream data signal when the voltage level of the downstream data signal is less than a predetermined threshold;  
 a means for activating and deactivating the amplification means; and  
 an attenuating means for attenuating the downstream data signal when the voltage level of the downstream data signal is greater than a predetermined threshold, the attenuating means being operative when the amplification means is deactivated.  
   
     
     
         8 . The transceiver circuit of  claim 7 , wherein 
 the amplification means further comprises a summing circuit having a receive operational amplifier, a feedback resistance, and an input resistance; and    the attenuating means further comprises the feedback resistance in series with the input resistance.    
     
     
         9 . The transceiver circuit of  claim 8 , wherein the receive means further comprises a transmission signal subtraction circuit coupling the transmission means to the summing circuit.  
     
     
         10 . The transceiver circuit of  claim 7 , further comprising measuring means for determining whether the voltage of the downstream data signal received by the transceiver circuit is greater than a predetermined threshold.  
     
     
         11 . The transceiver circuit of  claim 10 , further comprising means for triggering the activation/deactivation means responsive to the measuring means.  
     
     
         12 . The transceiver circuit of  claim 11 , wherein the means for triggering the activation/deactivation means is a switch.  
     
     
         13 . A method for receiving an downstream data signal in a transceiver circuit of a modem, comprising the steps of: 
 coupling a transmit circuit to primary winding in a line drive transformer;    coupling a receive circuit to the primary winding;    coupling a secondary winding of the line drive transformer to a local loop;    amplifying an downstream data signal with an amplifier having a first input resistance and a feedback resistance in the receive circuit when a voltage level of the downstream data signal is below a predetermined threshold;    attenuating the downstream data signal with a series resistance comprising the first input resistance and the feedback resistance, the amplifier being disabled when the voltage level is greater than or equal to the predetermined threshold.    
     
     
         14 . A transceiver circuit for a modem, comprising: 
 a line driver transformer defined by a primary winding and a secondary winding, the secondary winding being coupled to a local loop;    a line drive amplifier circuit coupled to the primary winding and configured to generate an upstream signal;    a receive circuit coupled to the primary winding and configured to receive an downstream signal, the receive circuit including: 
 an amplified signal pathway defined by a summing circuit having a receive operational amplifier configured to amplify the difference between a magnitude of the downstream signal and the upstream signal, the receive operational amplifier being coupled to both a first input resistance and a feedback resistance;  
 an attenuated signal pathway defined by a series connection between the first input resistance and the feedback resistance, the attenuated signal pathway configured to attenuate the downstream signal; and  
 a modem circuit responsive to a magnitude of the downstream signal to select one of the amplified signal pathway and the attenuated signal pathway as an operative signal pathway.  
   
     
     
         15 . The transceiver circuit of  claim 14 , wherein 
 the modem circuit further comprises a selection output electrically coupled to an enable/disable input of the receive operational amplifier, the selection output toggling the receive operational amplifier between an enabled state and a disabled state;    the amplified signal pathway being operative when the receive operational amplifier is in an enabled state; and    the attenuated signal pathway being operative when the receive operational amplifier is in a disabled state.    
     
     
         16 . The transceiver circuit of  claim 15 , wherein the modem circuit compares the magnitude of the downstream signal to a predetermined threshold.  
     
     
         17 . The transceiver circuit of  claim 16 , wherein 
 the modem circuit causes the receive operational amplifier to be placed in the enabled state when the downstream signal is below the predetermined threshold; and    the modem circuit causes the receive operational amplifier to be placed in the disabled state when the downstream signal is above the predetermined threshold.