Reducing second order distortion in an amplifier
View Patent ↗In an embodiment, an apparatus includes a component of a receiver path to receive and process an incoming signal. At least one element of the component is controllable based on a DC output of the component, to compensate for a second order intermodulation product of the apparatus. As one example, the component is a differential amplifier including a first transistor and a second transistor.
1. An apparatus comprising:
a differential amplifier including a first transistor and a second transistor, the differential amplifier coupled to receive an input radio frequency (RF) signal and to output an amplified RF signal, wherein at least one element of the differential amplifier is controllable based on a DC output of the differential amplifier, to compensate for a second order intermodulation product of the apparatus.
2. The apparatus of claim 1 , wherein the differential amplifier comprises a front end component of a radio receiver.
3. The apparatus of claim 1 , further comprising a controller to control a size of at least one of the first and second transistors based on the DC output of the differential amplifier.
4. The apparatus of claim 3 , wherein the differential amplifier comprises:
the first transistor having a first terminal to receive the input RF signal, wherein the input RF signal is a single-ended input RF signal; and
the second transistor having a first terminal to couple to a reference voltage node.
5. The apparatus of claim 3 , wherein the controller is to:
selectively disconnect the input RF signal from the first transistor;
determine a difference between a first voltage at a first output node coupled to a third terminal of the first transistor and a second voltage at a second output node coupled to a third terminal of the second transistor; and
adjust the size of the at least one of the first and second transistors based on the difference.
6. The apparatus of claim 5 , wherein the controller is to iteratively adjust the size until the difference reaches a target value.
7. The apparatus of claim 1 , wherein the differential amplifier further comprises a current source coupled to first and second transistors of the differential amplifier.
8. The apparatus of claim 7 , wherein the control of the controllable element is further to compensate for at least a portion of the second order intermodulation product caused by the current source.
9. The apparatus of claim 7 , further comprising:
a first degeneration resistor coupled between the first transistor and the current source; and
a second degeneration resistor coupled between the second transistor and the current source, wherein at least one of the first and second degeneration resistors comprises the at least one element controllable based on the DC output.
10. An apparatus comprising:
a differential amplifier to receive a first signal and to output an amplified differential signal at a differential output node, the differential amplifier having at least one controllable element, wherein the at least one controllable element is controlled to maintain a selected DC offset at the differential output node;
a controller to measure a DC offset at the differential output node and to control the at least one controllable element based at least in part on a comparison between the measured DC offset and the selected DC offset, wherein the controller is to control at least one of:
a size of a first transistor of the differential amplifier when the measured DC offset is greater than the selected DC offset and to control a size of a second transistor of the differential amplifier when the measured DC offset is less than the selected DC offset; and
a size of a degeneration resistor coupled between the first transistor and a current source of the differential amplifier based at least in part on the comparison.
11. The apparatus of claim 10 , wherein the differential amplifier comprises:
the first transistor having a first terminal to receive the first signal, wherein the first signal is a single-ended input radio frequency (RF) signal; and
the second transistor having a first terminal coupled to a reference voltage node.
12. The apparatus of claim 11 , wherein the at least one controllable element corresponds to the size of at least one of the first transistor and the second transistor of the differential amplifier, wherein maintenance of the selected DC offset is to compensate for a second order intermodulation product.
13. A method comprising:
measuring, during an initiation sequence of a receiver performed by a controller of the receiver, a difference between a first voltage at a first output node of a differential amplifier of the receiver and a second voltage at a second output node of the differential amplifier; and
adjusting, during the initiation sequence, a controllable element of the differential amplifier based on the difference until the difference reaches a target value.
14. The method of claim 13 , further comprising selectively disconnecting an input radio frequency (RF) signal obtained from an antenna coupled to the receiver from the differential amplifier prior to measuring the difference.
15. The method of claim 14 , further comprising thereafter switching the input RF signal to the differential amplifier.
16. The method of claim 13 , wherein adjusting the controllable element comprises adjusting a size of at least one of a first transistor and a second transistor of the differential amplifier.