The WM8940 is a low power, mono codec with integrated support for a differential or single ended mic, and includes drivers for speakers or headphone and mono line output. Advanced Delta Sigma converters are used along with digital decimation and interpolation filters to give high quality audio at sample rates from 8 to 48 ks/s. A selectable high pass filter and four fully programmable notch filters are available in the ADC path. An advanced mixed signal ALC function with noise gate is provided, while readback of PGA gain during ALC operation is supported. The digital audio interface supports A-law and μ-law companding. An on-chip PLL is provided to generate the required master clock from an external reference clock. The PLL clock can also be output if required elsewhere in the system.