Low voltage analog front end

A low voltage analog front end (AFE) suitable for converting an input voltage to a differential output current, comprising:

• first and second transistors having respective control inputs and respective current circuits controlled by said control inputs, said current circuits having respective output terminals and respective second terminals, said second terminals coupled to a ground point through respective first and second degeneration resistors, said second terminals otherwise electrically isolated from each other,
• first and second impedance networks each having first and second terminals, said first terminals connected to respective control inputs and said second terminals connected together at a common junction, and
• a current source, comprising:
• a current reference circuit connected between a supply voltage line and ground and arranged to conduct a reference current, and
• an output buffer circuit connected to said reference circuit and which includes a third degeneration resistor, said current reference circuit and output buffer circuit arranged to force voltages across the respective control input-current circuit circuits of said first and second transistors to cause said transistors to conduct respective DC bias currents which are about equal to the product of said reference current and the ratio of said third degeneration resistor value to said first and second degeneration resistor values, respectively,
• said first and second transistors arranged to conduct a differential output current which comprises a differential signal current that varies with an input voltage applied across said control inputs and is superimposed on said DC bias currents, said first and second transistors conducting said differential output current from their respective output terminals to said ground point via their respective second terminals, said arrangement of said transistors and said mirrored bias currents enabling said first and second impedance networks to primarily establish the input impedance across said control inputs and allowing said differential signal current to be conducted from said second terminals to said ground point without significantly affecting said input impedance.

A Gilbert mixer circuit, comprising:

• an input stage, comprising:
• first and second transistors having respective control inputs and respective current circuits controlled by said control inputs, said current circuits having respective output terminals and respective second terminals, said second terminals coupled to a ground point through respective first and second degeneration resistors, said second terminals otherwise electrically isolated from each other,
• first and second impedance networks each having first and second terminals, said first terminals connected to respective ones of said transistor control inputs and said second terminals connected together at a common junction, and
• a current source connected to said common junction and arranged to cause respective DC bias currents to be mirrored through respective ones of said transistor current circuits,
• said first and second transistors arranged to conduct a differential output current which comprises a differential signal current that varies with an input voltage applied across said control inputs and is superimposed on said DC bias currents, said first and second transistors conducting said differential output current from their respective output terminals to said ground point via their respective second terminals, said arrangement of said transistors and said mirrored bias currents enabling said first and second impedance networks to primarily establish the input impedance across said control inputs and allowing said differential signal current to be conducted from said second terminals to said ground point without significantly affecting said input impedance;
• and
• an output stage having two current outputs, said output stage connected to receive said differential output current and which alternately switches said differential output current between said output stage current outputs in response to an alternating control voltage.