Hybrid frequency compensation network
View Patent ↗Hybrid frequency compensation is provided. Hybrid circuits are used to subtract the transmit signal from the receive signal in a full duplex communication system. Since the hybrid circuit and the main line driver are exposed to different loads, accurate subtraction is difficult to achieve. A frequency dependent network is used to match the loading seen by the driver and the hybrid. The compensation network can be based on active and/or passive components.
1. A hybrid circuit comprising:
a driver circuit configured to receive a differential input signal, wherein the differential input signal includes first and second input signals, wherein the driver circuit is further configured to buffer the differential input signal to generate a first signal for transmission to a load, wherein the first signal is based, at least in part, on the differential input signal, wherein the driver circuit includes a first driver circuit configured to receive the first input signal and a second driver circuit configured to receive the second input signal, and wherein at least one of the first or second driver circuits comprises a transistor further configured to receive at least one of the first or second input signals at a gate terminal;
a terminal coupled to the driver circuit and configured to provide the first signal to the load and receive a second signal through the load, wherein the first and second signals are respectively provided and received at least partially simultaneously;
a replica circuit configured to receive the differential input signal, at least partially replicate an operation of the driver circuit, and generate an output signal, wherein the replica circuit includes a first replica circuit configured to receive the first input signal and a second replica circuit configured to receive the second input signal;
a load replica coupled to the replica circuit, wherein the load replica has an impedance based, at least in part, on an impedance of the load, wherein the load replica is configured to receive the output signal and generate an adjusted output signal, and wherein the load replica includes a first load replica coupled between an output of the first driver circuit and an output of the second replica circuit and a second load replica coupled between an output of the second driver circuit and an output of the first replica circuit; and
a combiner coupled to the terminal and the load replica and configured to subtract the adjusted output signal from a combination of the first and second signals received at the terminal.
2. The hybrid circuit of claim 1 , wherein the adjusted output signal is approximately equal to the first signal.
3. The hybrid circuit of claim 1 , wherein the combiner is further configured to generate an approximation of the second signal based, at least in part, on the subtraction of the adjusted output signal from the combination of the first and second signals.
4. The hybrid circuit of claim 1 , wherein the impedance of the load replica is approximately equal to the impedance of the load.
5. The hybrid circuit of claim 1 , wherein the load replica is further configured to match loading seen by the driver circuit.
6. The hybrid circuit of claim 1 , wherein the load replica comprises an adjustable capacitor.
7. The hybrid circuit of claim 1 , wherein the load replica comprises an adjustable resistor.
8. The hybrid circuit of claim 1 , wherein the load replica is further coupled to the terminal.
9. The hybrid circuit of claim 1 , wherein the transistor is a first transistor, and wherein the replica circuit further comprises a second transistor further configured to receive at least a portion of the differential input signal at a gate terminal.