Low distortion single-to-differential wide-band variable gain amplifier for optical communications

A circuit, comprising:

• a photodiode configured to receive an optical signal and convert the optical signal into an electrical signal;
• and
• one or more variable gain amplifiers configured to receive the electrical signal or a variant thereof and amplify the received electrical signal or the variant thereof, wherein each of the one or more variable gain amplifiers comprise:
• a first transistor;
• a second transistor;
• and
• an N-type Metal-Oxide-Semiconductor (NMOS) resistor switch connected between the first and second transistors, wherein the NMOS resistor switch is configured to operate in a triode region when an input voltage at a base of the first switch is greater than an input voltage at a base of the second switch, wherein the NMOS resistor switch is also configured to operate in the triode region when the input voltage at the base of the first switch is less than the input voltage at the base of the second switch, and wherein at least one of the one or more variable gain amplifiers comprise a Direct Current (DC)-blocking capacitor connected between a base of the first transistor and a gate of the NMOS resistor switch thereby blocking a common-mode bias voltage on the first switch from reaching a gate voltage of the NMOS resistor switch.

An optical communication system, comprising:

• an analog front end comprising one or more variable gain amplifiers, the one or more variable gain amplifiers comprising:
• a first transistor;
• a second transistor;
• and
• an N-type Metal-Oxide-Semiconductor (NMOS) resistor switch connected between the first and second transistors, wherein the NMOS resistor switch is configured to operate in a triode region when an input voltage at a base of the first switch is greater than an input voltage at a base of the second switch, wherein the NMOS resistor switch is also configured to operate in the triode region when the input voltage at the base of the first switch is less than the input voltage at the base of the second switch, and wherein at least one of the one or more variable gain amplifiers comprise a Direct Current (DC)-blocking capacitor connected between a base of the first transistor and a gate of the NMOS resistor switch thereby blocking a common-mode bias voltage on the first switch from reaching a gate voltage of the NMOS resistor switch.