RESISTOR ATTENUATOR WITH SWITCH DISTORTION CANCELLATION

摘要

A programmable (multistep) resistor attenuator includes distortion cancellation for harmonic distortion currents. The attenuator includes at last one attenuation stage coupled between a signal input node and a virtual ground node (such as an input to a differential amplifier). The attenuation node is: (a) coupled to the input node through a resistor R; (b) coupled to the virtual ground node through a resistor kR and a virtual ground switch Swf with an on resistance Rswf; and (c) coupled to a differential ground through a resistor mR and a differential ground switch Swp with an on resistance Rswp. Swp is sized relative to Swf such that, when both Swp and Swf are conducting, a component Ipnf of a current Ipn through Rswp and mR to the attenuation node and branching into kR and Rswf, matches, in phase and magnitude, a harmonic current Ifn from the virtual ground through Rswf and kR to the attenuation node, thereby substantially canceling the harmonic distortion appearing at the virtual ground. Distortion cancellation can be based on cancellation is based on matching switches Swf and Swp and the resistors R, mR, kR, and hence is insensitive to PVT variations, input frequency and amplitude. an optimum ratio of Rswp and Rswf is a function of only a ratio of resistors, and hence is insensitive to values of Rswp and Rswf. The attenuator architecture is extendable to multistage configurations.

主权项

1. A resistor attenuator circuit suitable for programmable attenuation of an input signal, comprising
an input node coupled to receive the input signal; an virtual ground node configured as a virtual ground; at least one attenuation stage coupled at an attenuation node to the input node and the virtual ground node, the attenuation node
coupled to the input node through a resistor R,coupled to the virtual ground node through a resistor kR and a virtual ground switch Swf with an on resistance Rswf, andcoupled to a differential ground through a resistor mR and a differential ground switch Swp with an on resistance Rswp; Swp is sized relative to Swf such that, when both Swp and Swf are conducting, a component Ipnf of a current Ipn through Rswp and mR to the attenuation node and branching into kR and Rswf, matches, in phase and magnitude, a harmonic current Ifn from the virtual ground through Rswf and kR to the attenuation node, thereby substantially canceling the harmonic distortion appearing at the virtual ground.