PCM CODECs Keep S/N Ratios Low In Portable Communications Applications

Well-suited for digital cellular telephones such as GSM, CDMA and TDMA and other portable communications applications, the BU8731KV and BU8733KV linear PCM CODEC ICs have a signal-to-noise ratio that's said to be better than many other such devices. Typical operating current for the BU8733KV is 5.4 mA, while 8 mA is typical for the BU8731KV. Both ICs draw just 0.1 µA in standby mode, and individual blocks in the chips can be powered down when not in use. Features include a 14-bit linear or µ/A-law CODEC, an on-board DTMF and tone-generating melodies for the ringer. The DTMF and tone-generator functions are designed to off-load the system DSP. The DSP interface of the BU8733KV is compatible with all major DSPs. The system clock for both ICs is generated from an 8 kHz frame synchronous signal as part of the PLL unit. In the BU8731KV, the PCM data-transfer clock can be adjusted externally between 64 kHz (128-kHz linear) to 2048 kHz. Also included are microphone and BTL-mode speaker amplifiers that can direct drive 32 ohm dynamic earpieces without an external amplifier.