Voltage to current converter with minimal noise sensitivity

Abstract

A voltage to current (V-I) converter includes a low pass filter, a first converting element, a second converting element, and an output. The low pass filter receives an input voltage signal and outputs a filtered voltage signal. The output of the low pass filter is fed to the first converting element, which converts the filtered voltage signal into a corresponding output current which is fed to the output of the V-I converter. Preferably, the voltage to current gain of the first converting element is high. The low pass filter and the first converting element form a low frequency or DC signal path. The V-I converter further includes a second converting element, which receives the input voltage signal and converts it into a corresponding output current which is also fed to the output of the V-I converter. This current is combined with the output current from the first converting element to produce an overall output current. Preferably, the second converting element has a substantially flat frequency response and a low voltage to current gain relative to the voltage to current gain of the first converting element. The second converting element forms the high frequency or alternating current (AC) signal path. By implementing a high gain on the low frequency path and a low gain on the high frequency path, the high frequency noise components are insignificant relative to the low frequency components. Thus, a relatively mall input voltage range is converted into a relatively large output current range without suffering increased sensitivity to noise.