Programmable Digital Voice Filters and Flexible Clocking Scheme Eliminates PLLs and Crystal Oscillators

The MAX9860 includes two differential microphone inputs with a user-programmable preamplifier and programmable gain amplifier. Automatic gain control with selectable attack/release times and a signal threshold allows maximum dynamic range. A noise gate with a selectable threshold helps quiet the audio channel when no signal is present. This configuration allows the user to select one channel for voice, while the other channel can be converted and processed downstream for echo-noise canceling and background noise.

The programmable digital voice filters provide full attenuation for out-of-band signals, as well as a 5th-order, GSM-compliant digital highpass filter. An elliptical digital filter notches the 217Hz (GSM) frequency for 8kHz and 16kHz sample rates. Also, an available digital side-tone mixer provides loopback of the ADC signal (microphones) to the DAC output (headphone) in the case of a headset application.

The analog output is a bridge-tied-load (BTL), mono headphone amplifier. The MAX9860 can output 30mW into a 32ohm earpiece while operating from a single 1.8V power supply. This low-voltage operation translates into low power consumption that makes the MAX9860 the ideal choice for battery-powered applications.

The MAX9860 includes two serial data interfaces. The ADC and DAC data is transferred over a flexible digital I2S-compatible interface that also supports TDM mode. General mode settings, including volume control, digital filters, and shutdown, are all programmed through a 2-wire, I2C-compatible interface.