6

4904A–DAB–03/06

ATR2731

3.

Functional Description

The ATR2731 represents a monolithically integrated front-end IC designed for applications in

DAB receivers. It covers RF and IF signal processing, the PLL section and also supporting func-

tions such as D/A converters or switching outputs.

Two RF input ports offer the possibility of handling various input signals such as a down-con-

verted L-band signal or band II and band III RF signals. The high dynamic range of the RF inputs

and the use of a gain-controlled amplifier and a gain-controlled mixer in the RF section offer the

possibility of handling even strong RF input signals. The LO signal of the first mixer stage is

derived from an on-chip VCO. The VCO frequency is either divided by two or directly fed to the

mixer. In this way band II and band III can be covered easily.

In the IF section, it can be selected if the first IF signal is down-converted to a second, lower IF

or if it is simply amplified to appear at the IF output. If the down-conversion option is chosen, it

can be selected if the LO signal of the IF mixer is directly derived from the reference signal of the

PLL, or if it is generated by doubling its frequency. The amplifiers in the IF section are gain-con-

trolled in similar fashion to the RF section.

The RF and the IF part also contain AGC functional blocks which generate the AGC control volt-

ages. The AGC thresholds can be defined by means of three on-chip 4-bit D/A converters.

The frequency of the VCO is locked to a reference frequency by an on-chip fractional-N PLL cir-

cuit which guarantees a superior phase-noise performance. The reference frequency is

generated by an on-chip crystal oscillator which can also be overdriven by an external signal.

Starting from a minimum value, the reference scaling factor is freely programmable.

Three switching outputs can be used for various switching tasks on the front-end board. Three

8-bit D/A converters providing an output voltage between 0V and 8.5V are used to improve the

tuning voltages of the tuned preselectors which are derived from the tuning voltage of the VCO.