Out in Front: July 18, 1996

A 14-bit, 100M-sample/sec DAC features intermodulation specifications designed for applications such as multiplexing voice channels for TDMA and CDMA cellular systems. The Harris HI5741 DAC simultaneously converts 20 voice-subcarrier channels and yields a worst-case distortion product 70 dB below the IF subcarrier peak level, or "multitone power ratio" (MTPR). For 10 tones, the corresponding MTPR figure is -76 dBc. The company performed the 20-tone test with tones spaced from 700 kHz to 5.7 MHz and with the DAC clocked at 13 MHz.

Although many applications are satisfied with DACs that process just one, two, or three tones at once, a software-driven base station for digital voice communications must multiplex more signals. The more signals that the DAC handles simultaneously, the fewer baseband-to-IF signal paths an application needs. For example, a Global System for Mobile communications (GSM) base station may multiplex twelve 200-kHz-wide RF channels; by using a multitone DAC, your design requires only one baseband-to-IF chain.

Spurious-free dynamic range for this DAC, a useful though not as application-specific parameter, is 86 dBc. The 28-lead HI5741 requires 5 and -5.2V supplies, provides 20.48-mA output current at full scale, and has TTL/CMOS-compatible digital inputs. The HI5741 comes in plastic DIP and SOIC packages and costs $49.90 (1000).

—by Bill Schweber

Harris Semiconductor Corp, Melbourne, FL. (800) 442-7747, ext 7566, http://www.semi.harris.com.