Apparatus and methods for biasing low noise amplifiers
Apparatus and methods for biasing low noise amplifiers are provided herein. In certain configurations, a low noise amplifier (LNA) includes an input, an output, a transconductance device, a cascode device, a bias current source, and a feedback bias circuit. The transconductance device generates an amplified signal by amplifying an input signal received at the input, and provides the amplified signal to the output via the cascode device. The bias current source generates a bias current that flows through the cascode device and the transconductance device. The feedback bias circuit provides feedback from the LNA's output to the LNA's input to control an input bias voltage of the transconductance device.
1. A low noise amplifier comprising:
a cascode device;
a transconductance device configured to generate an amplified signal based on amplifying an input signal received at an input node, the transconductance device further configured to provide the amplified signal to an output node via the cascode device;
a bias current source configured to generate a bias current that flows through the cascode device and the transconductance device, the bias current source, the cascode device, and the transconductance device electrically connected in series with one another with the cascode device between the bias current source and the transconductance device; and
a feedback bias circuit configured to control an input bias voltage of the transconductance device based on providing feedback from the output node to the input node.
2. The low noise amplifier of claim 1 wherein the transconductance device and the cascode device are bipolar transistors.
3. The low noise amplifier of claim 1 wherein the transconductance device and the cascode device are field-effect transistors.
4. The low noise amplifier of claim 1 wherein the feedback bias circuit includes a first biasing resistor electrically between the input node and a first voltage, and a second biasing resistor electrically connected between the input node and the output node.
5. The low noise amplifier of claim 4 wherein the feedback bias circuit further includes a third biasing resistor configured to bias the cascode device based on a voltage of the output node.
6. The low noise amplifier of claim 1 wherein the feedback bias circuit includes a bias diode electrically connected along a feedback path from the output node to the input node.
7. The low noise amplifier of claim 6 wherein the feedback bias circuit further includes a first radio frequency isolation resistor electrically connected between the input node and a cathode of the bias diode, and a second radio frequency isolation resistor electrically connected between the output node and an anode of the bias diode.
8. The low noise amplifier of claim 7 wherein the feedback bias circuit further includes a current controlling resistor electrically connected between the input node and a first voltage.
9. The low noise amplifier of claim 6 wherein the bias diode is a diode-connected transistor.
10. The low noise amplifier of claim 1 wherein the current source controls the bias current to be substantially proportional to absolute temperature.
11. The low noise amplifier of claim 10 wherein the current source includes a p-type field-effect transistor and a proportional to absolute temperature circuit that controls a gate voltage of the p-type field-effect transistor.
12. The low noise amplifier of claim 1 further comprising a mid-node impedance network electrically connected along a signal path of the low noise amplifier between the transconductance device and the cascode device.
13. A radio frequency front-end system comprising:
a low noise amplifier including a cascode device, a transconductance device, a bias current source configured to generate a bias current that flows through the cascode device and the transconductance device, and a feedback bias circuit, the transconductance device configured to generate an amplified radio frequency signal based on amplifying an input radio frequency signal received at an input node and to provide the amplified radio frequency signal to an output node via the cascode device, and the feedback bias circuit configured to control an input bias voltage of the transconductance device based on providing feedback from the output node to the input node;
a bypass path;
a power amplifier; and
an input switch including a first throw for providing the radio frequency input signal to the low noise amplifier, a second throw electrically connected to the bypass path, and a third throw electrically connected to the power amplifier.
14. The radio frequency front-end system of claim 13 wherein the feedback bias circuit includes a first biasing resistor electrically between the input node and a first voltage, and a second biasing resistor electrically connected between the input node and the output node.
15. The radio frequency front-end system of claim 13 wherein the low noise amplifier further includes a mid-node impedance network electrically connected between the transconductance device and the cascode device.
16. A wireless communication device comprising:
a low noise amplifier including a cascode device, a transconductance device, a bias current source configured to generate a bias current that flows through the cascode device and the transconductance device, and a feedback bias circuit, the transconductance device configured to generate an amplified radio frequency signal based on amplifying an input radio frequency signal received at an input node and to provide the amplified radio frequency signal to an output node via the cascode device, and the feedback bias circuit configured to control an input bias voltage of the transconductance device based on providing feedback from the output node to the input node, the bias current source, the cascode device, and the transconductance device electrically connected in series with one another with the cascode device between the bias current source and the transconductance device; and
an antenna configured to receive the input radio frequency signal.
17. The wireless communication device 16 wherein the feedback bias circuit includes a first biasing resistor electrically between the input node and a first voltage, and a second biasing resistor electrically connected between the input node and the output node.
18. The wireless communication device 16 wherein the low noise amplifier further includes a mid-node impedance network electrically connected between the transconductance device and the cascode device.
19. The wireless communication device 16 wherein the feedback bias circuit includes a first isolation resistor, a bias diode, and a second isolation resistor electrically connected in series along a feedback path from the output node to the input node, the bias diode between the first isolation resistor and the second isolation resistor.
20. The low noise amplifier of claim 1 further comprising an inductor electrically connected in series with the bias current source between a power supply voltage and the output node.