Introduction
This application note is a guide to understanding and implementing the digital hybrid feature found in Si305x DAA products. The Si305x contains an on-chip analog hybrid that performs the 2- to 4-wire conversion and near-end echo cancellation. This hybrid circuit is adjusted for each ac termination setting selected to achieve a minimum transhybrid balance of 20 dB. The Si305x also offers a digital filter for additional near-end echo cancellation to compensate for any line impedance mismatch. For each ac termination setting, the eight programmable hybrid registers (Registers 45- 52) can be programmed with coefficients to increase the cancellation under real-world line conditions. This digital filter can produce 10 dB or greater of near-end echo cancellation in addition to the 20 dB from the analog hybrid circuitry.