Low-loss impedance-matched source-follower for repeating or switching signals on a high speed link

A circuit for switching or repeating signals on a differential signal high speed link comprising:

• a differential input comprising positive input and negative input for coupling to differential input transmission lines for the high speed link;
• a differential output comprising positive output and negative output for coupling to differential output transmission lines for the high speed link;
• a first termination resistor coupling the positive input to a termination voltage;
• a second termination resistor coupling the negative input to the termination voltage;
• a first transistor, having first gate, source and drain terminals, configured as a source follower wherein the first gate terminal is coupled to the positive input, the first source terminal is coupled to the positive output and the first drain terminal is coupled to a voltage source;
• a second transistor, having second gate, source and drain terminals, configured as a source follower wherein the second gate terminal is coupled to the negative input, the second source terminal is coupled to the negative output and the second drain terminal is coupled to the voltage source;
• and
• a bias current circuit coupled to the first and second source terminals and the positive and negative outputs for providing bias currents for the first and second transistors resulting in essentially constant output impedance over process, voltage and temperature variations.

A system for switching or repeating signals on a high speed link comprising:

• a high speed link comprising input and output transmission lines;
• a transmitter coupled to the input transmission line;
• a receiver coupled to the output transmission line;
• and
• a circuit coupled between the input and output transmission lines for switching or repeating signals transmitted onto the input transmission line by the transmitter, the circuit comprising:
• an input and an output for coupling, respectively, to the input and output transmission lines;
• a termination resistor coupling the input to a termination voltage;
• a first transistor, having first gate, source and drain terminals, configured as a source follower wherein the first gate terminal is coupled to the input, the first source terminal is coupled to the output and the first drain terminal is coupled to a voltage source;
• and
• a bias current circuit coupled to the first source terminal and output for providing bias current for the first transistor resulting in essentially constant output impedance over process, voltage and temperature variations.