A digitally controlled 8-input/2-output audio mixer IC

An integrated-circuit implementation of an eight channel audio mixer is presented. This architecture utilizes a novel cascaded R-xR ladder. The requirements for such an IC have emerged to satisfy a generic need for such a function, particularly in professional audio and multimedia systems. Specifically, the IC described is an 8×2 mixer-eight voltage inputs and two voltage outputs. Each input has an attenuation control with 1 dB steps up to 63 dB maximum attenuation and can be steered to either, both or neither (mute) left/right output mixers. Design considerations are presented for optimum Total Harmonic Distortion (THD) and the particular design achieves a THD of 0.01%. The chip has been implemented on an advanced BiCMOS process with complementary MOS, bipolar transistors and oxide capacitors in an area of less than 12.5 mm²