1997-10-03 , E/IC-844/410
Technical Backgrounder From Philips Semiconductors

The UBA1707 is a true single-chip solution to all the line interface and analog speech-processing functions required in digital answering machines and cordless telephone basestations.

To meet the specific requirements of telephone standards worldwide, its line interface can be programmed into voltage or current regulation modes, with independent control of the equipment's DC and AC set impedance. Line current controlled AGC functions in both the transmit and receive channels, featuring programmable AGC range and slope, provide automatic line loss compensation over an exceptionally wide range of exchange supply voltages and feeding bridge resistances. Operation at DC line voltages as low as 1.2 V allows several telephones to operate in parallel on the same line. To eliminate the reliability problems associated with mechanical relays, drive circuitry for an external solid-state hook switch provides fully electronic on/off hook switching, pulse dialling and register recall (timed loop break).

In addition to its programmable line interface functions, the UBA1707 also brings all the baseband audio transmit/receive functions required in cordless phone basestations, digital answering machines and fax machines under digital control. The transmit amplifier of the UBA1707 handles input signals with amplitudes of several hundred millivolts (typically up to 350 mV with a line current of 15 mA or up to 750 mV with a line current of 90 mA for less than 2% THD), while a separate on-chip auxiliary microphone amplifier provides the talk facilities required for features such as an intercom or baby-alarm.

The UBA1707's integral loudspeaker amplifier features two selectable input channels, 3-bit volume control, rail-to-rail output voltage swing and smooth dynamic output limiting, plus automatic gain reduction if the supply voltage falls below 2.7 V. Each input handles signals up to 500 mV rms for less than 2% THD and the output drives loudspeaker loads down to 8 ohms at 3.3 V or 16 ohms at 5 V. The result is exceptionally high quality sound reproduction.

Separate device pins for the two loudspeaker amplifier inputs, as well as for the auxiliary amplifier input and output, give designers maximum FLEXibility in the use of these function blocks within the equipment.

The UBA1707 is programmed via 4 on-chip registers that control the current/voltage regulation mode, AGC range and slope, loudspeaker volume and channel selection, dynamic limiting, amplifier muting and various power down modes. Register programming is via the industry-standard 3-wire serial control bus. In addition, the UBA1707 includes three general- purpose switches that are controlled via the 3-wire bus, which can be used for functions such as on/off LED switching.

The UBA1707 is available in a 28-lead small-outline or ultra space-saving 28-lead shrink small outline package and is manufactured in Philips Semiconductors' advanced BiMOS IC process in Caen, France. In a volume of 1 million pieces per year the SO28 packaged device sells for around US$ 1.15.

Philips Semiconductors, a division of Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the ninth largest semiconductor supplier in the world and the third largest supplier of discretes in the world. Philips Semiconductors' innovations in digital audio, video, and mobile technology position the company as a leader in the consumer, multimedia and wireless communications markets. Sales offices are located in all major markets around the world and are supported by systems labs.