Time gain compensation circuit in an ultrasound receiver

Abstract

The disclosure provides a time gain compensation (TGC) circuit. The TGC circuit includes an impedance network. A differential amplifier is coupled to the impedance network. The differential amplifier includes a first input port, a second input port, a first output port and a second output port. A first feedback resistor is coupled between the first input port and the first output port. A second feedback resistor is coupled between the second input port and the second output port. The impedance network provides a fixed impedance to the differential amplifier when a gain of the TGC circuit is changed from a maximum value to a minimum value.

What is claimed is: 
     
         1 . A time gain compensation (TGC) circuit comprising:
 an impedance network;   a differential amplifier coupled to the impedance network, the differential amplifier comprising a first input port, a second input port, a first output port and a second output port;   a first feedback resistor coupled between the first input port and the first output port; and   a second feedback resistor coupled between the second input port and the second output port, wherein the impedance network provides a fixed impedance to the differential amplifier when a gain of the TGC circuit is changed from a maximum value to a minimum value.   
     
     
         2 . The TGC circuit of  claim 1 , wherein the impedance network provides the fixed impedance to the differential amplifier when the gain of the TGC circuit is changed from the minimum value to the maximum value. 
     
     
         3 . The TGC circuit of  claim 1 , wherein the differential amplifier is at least one of an operational amplifier and a high gain amplifier. 
     
     
         4 . The TGC circuit of  claim 1 , wherein a feedback factor and a bandwidth of the differential amplifier are constant when the gain of the TGC circuit is changed. 
     
     
         5 . The TGC circuit of  claim 1 , wherein the impedance network comprises one or more voltage controlled resistors. 
     
     
         6 . The TGC circuit of  claim 1 , wherein the impedance network further comprises:
 a first fixed resistor coupled to a first node and configured to receive a positive input voltage;   a second fixed resistor coupled to a second node and configured to receive a negative input voltage;   a first voltage controlled resistor coupled between the first node and the second node;   a second voltage controlled resistor coupled between the first node and the first input port; and   a third voltage controlled resistor coupled between the second node and the second input port.   
     
     
         7 . The TGC circuit of  claim 1 , wherein a change in the gain of the TGC circuit provides a corresponding change in a resistance values of the first voltage controlled resistor, the second voltage controlled resistor and the third voltage controlled resistor, such that the impedance network provides the fixed impedance to the differential amplifier. 
     
     
         8 . A method of controlling an output of a time gain compensation (TGC) circuit when a gain of the TGC circuit is changed from a maximum value to a minimum value, the method comprising:
 decreasing a resistance value of a first voltage controlled resistor;   increasing a resistance values of a second voltage controlled resistor and a third voltage controlled resistor; and   maintaining a resistance values of a first fixed resistor and a second fixed resistor such that a fixed impedance is provided to a differential amplifier.   
     
     
         9 . The method of  claim 8  further comprising:
 increasing the resistance value of the first voltage controlled resistor; 
 decreasing the resistance values of the second voltage controlled resistor and the third voltage controlled resistor; and 
 maintaining the resistance values of the first fixed resistor and the second fixed resistor such that the fixed impedance is provided to the differential amplifier when the gain of the TGC circuit is changed from the minimum value to the maximum value. 
 
     
     
         10 . The method of  claim 8  further comprising maintaining a feedback factor and a bandwidth of the differential amplifier constant when the gain of the TGC circuit is changed. 
     
     
         11 . The method of  claim 8  further comprising receiving a positive input voltage at the first fixed resistor and receiving a negative input voltage at the second fixed resistor. 
     
     
         12 . The method of  claim 8 , wherein the first voltage controlled resistor, the second voltage controlled resistor, the third voltage controlled resistor, the first fixed resistor and the second fixed resistor form an impedance network, and wherein the impedance network is coupled to the differential amplifier. 
     
     
         13 . The method of  claim 8 , wherein an output of the differential amplifier is the output of the TGC circuit, and the impedance network provides the fixed impedance to the differential amplifier when the gain of the TGC circuit is changed. 
     
     
         14 . The method of  claim 8 , wherein the differential amplifier is at least one of an operational amplifier and a high gain amplifier. 
     
     
         15 . An ultrasound system comprising:
 a transmitter configured to transmit a pulse signal;   a receiver configured to receive one or more reflected electrical signals, the receiver comprising a plurality of processing chains, at least one processing chain of the plurality of processing chains comprising:
 a low noise amplifier (LNA) configured to receive one of the one or more reflected electrical signals as an input signal and to generate an amplified signal; and 
 a time gain compensation (TGC) circuit configured to receive the amplified signal, the TGC circuit comprising:
 an impedance network; 
 a differential amplifier coupled to the impedance network, the differential amplifier comprising a first input port, a second input port, a first output port and a second output port; and 
 a first feedback resistor coupled between the first input port and the first output port; and 
 a second feedback resistor coupled between the second input port and the second output port, wherein the impedance network provides a fixed impedance to the differential amplifier when a gain of the TGC circuit is changed from a maximum value to a minimum value. 
 
   
     
     
         16 . The ultrasound system of  claim 15  further comprising:
 a filter configured to receive an output of the TGC circuit and configured to generate a filtered output, the output of the TGC circuit is generated at the first output port and the second output port; 
 an analog to digital converter (ADC) configured to generate a digital data in response to the filter output; and 
 a processor coupled to the ADC and configured to process the digital data. 
 
     
     
         17 . The ultrasound system of  claim 15 , wherein the differential amplifier is at least one of an operational amplifier and a high gain amplifier. 
     
     
         18 . The ultrasound system of  claim 15 , wherein a feedback factor and a bandwidth of the differential amplifier are constant when the gain of the TGC circuit is changed. 
     
     
         19 . The ultrasound system of  claim 15 , wherein the impedance network further comprises:
 a first fixed resistor coupled to a first node and configured to receive a positive input voltage;   a second fixed resistor coupled to a second node and configured to receive a negative input voltage;   a first voltage controlled resistor coupled between the first node and the second node;   a second voltage controlled resistor coupled between the first node and the first input port; and   a third voltage controlled resistor coupled between the second node and the second input port.   
     
     
         20 . The ultrasound system of  claim 15 , wherein a change in the gain of the TGC circuit provides a corresponding change in a resistance values of the first voltage controlled resistor, the second voltage controlled resistor and the third voltage controlled resistor, such that the impedance network provides the fixed impedance to the differential amplifier.