The U2731B is a monolithically integrated Digital Audio Broadcasting one-chip front end circuit manufactured using Atmel's advanced UHF5S technology. Its functionality covers a gain-controlled RF amplifier with two selectable RF inputs, a gain-controlled RF mixer, a VCO which provides the LO signal for the RF mixers, either directly or after passing a frequency divider, a SAW filter driver, an AGC block for the RF section, a gain-controlled IF amplifier, an IF mixer which can also be bypassed, an AGC block for the IF section and a fractional-N frequency synthesizer. The frequency synthesizer controls the VCO to synthesize frequencies in the range of 70 MHz to 500 MHz in a 16-kHz raster; within certain limits the reference divider factor is fully programmable. The lock status of the phase detector is indicated at a special output pin; three switching outputs can be addressed. A reference signal which is generated by an on-chip reference oscillator is available at an output pin. This reference signal is also used to generate the LO signal for the IF mixer, either by doubling the frequency or by using the reference frequency itself. Three D/A converters at a resolution of 8 bits provide a digitally controllable output voltage. The thresholds inside the AGC blocks can be digitally controlled by means of on-chip 4-bit D/A converters. All functions of this IC are controlled via a simple two-wire bus.