1. A circuit for automatically selecting a low noise frequency for use in a device comprising: a plurality of sense channels, each sense channel configured to receive a signal from a touch sensor panel; a summing circuit coupled to the plurality of sense channels and configured to generate a sum of the signals; a pair of magnitude circuits coupled to the summing circuit, one of the pair of magnitude circuits coupled to the summing circuit through a first mixer configured for demodulation with an in-phase (I) component of a demodulation frequency so as to calculate an in-phase magnitude value corresponding to an amount of noise at the demodulation frequency, and the other of the pair of magnitude circuits coupled to the summing circuit through a second mixer configured for demodulation with a quadrature (Q) component of the demodulation frequency so as to calculate a quadrature magnitude value corresponding to the amount of noise at the demodulation frequency; and frequency selection logic coupled to the pair of magnitude circuits and configured to select without intervention from a processor the demodulation frequency as a low noise frequency if the amount of noise is lower than an amount of noise at another demodulation frequency, wherein the processor is configured to identify one or more touch events on the touch sensor panel.