Analog bias control of RF amplifiers
Examples provide methods and apparatus for controlling a DC bias current in an RF amplifier. In one example where the RF amplifier is implemented on an amplifier die, a reference voltage is produced across a reference resistor implemented on the amplifier die, the DC bias current is measured, and a current controller, which is implemented on a controller die that is separate from the amplifier die, operates a feedback loop using the reference voltage to control a level of the DC bias current.
1. An amplifier module comprising:
a radio frequency (RF) amplifier;
a current sensing resistor connected to the RF amplifier, a sense voltage measured across the current sensing resistor being indicative of a DC bias current in the RF amplifier;
a reference resistor; and
a current controller including a current source and a feedback amplifier, the feedback amplifier having an output connected to a gate node of the RF amplifier, a first input connected to the reference resistor, and a second input connected to the current sensing resistor, the current source being configured to apply a first current to the reference resistor to produce a reference voltage at the first input of the feedback amplifier, the feedback amplifier being configured to produce a control voltage at the gate node to drive the RF amplifier to adjust the DC bias current to equalize the sense voltage and the reference voltage.
2. The amplifier module of claim 1 wherein the output of the feedback amplifier is connected to the gate node of the RF amplifier via a gate resistor.
3. The amplifier module of claim 1 wherein the RF amplifier, the current sensing resistor, and the reference resistor are implemented on an amplifier die, and wherein the current controller is implemented on a controller die separate from the amplifier die.
4. The amplifier module of claim 1 wherein the current controller includes a first filter connected to the output of the feedback amplifier.
5. The amplifier module of claim 4 wherein the first filter includes a first series resistor connected between the output of the feedback amplifier and the gate node, and a first shunt capacitor connected between the first series resistor and ground.
6. The amplifier module of claim 1 wherein the RF amplifier is a differential amplifier.
7. The amplifier module of claim 1 wherein the current controller includes chopper circuitry coupled to the feedback amplifier and configured to reduce an offset voltage of the feedback amplifier.
8. The amplifier module of claim 1 wherein the current controller has at least one user-adjustable parameter, and wherein the current controller includes a control input configured to receive a control signal to adjust the at least one user-adjustable parameter.
9. The amplifier module of claim 1 wherein the current source is programmable and wherein a value of the first current is controllable via a programming interface connected to the current source.
10. The amplifier module of claim 1 wherein the current controller includes a control input configured to receive a control signal, and wherein a value of the first current is trimmable via the control signal.