TUA6120

The TUA6120 'TORNADO' is a direct conversion receiver for digital QPSK or 8PSK Sat receiving systems in BICMOS
technology.

Compared to the conventional superheterodyne receiver the DCR architecture eliminates expensive RF-filters for image rejection and IF-filters for channel selection. Instead there are on-chip filters with selectable bandwidth integrated. The DCR system is the most promising approach for low-cost digital set-top boxes front ends.Via a LNA input stage, the RF signal is split into two rails. One is the buffered loopthrough RF output and, the other goes through a PGA (Programmable Gain Amplifier) to the I/Q- Mixers.

The signal of the synthesizer VCO is multiplied to 4 x RF input frequency by an internal 3.8-8.6 GHz PLL system. To drive the mixers, this 3.8-8.6 GHz signal is split into quadrature components by a digital divider by 4.

The VCO from which the oscillator signal is derived, never runs at the input frequency.The mixers are followed by 2 matched base-band PGA's and filters. The filter roll-off is selectable by software. Behind the filters external coupling capacitors eliminate undesired DC-components. Then follow another two base-band amplifiers and output buffers. The gain of the Q base-band amplifier is adjustable for compensation of I/Q gain impairment.

The AGC detector senses the output level and generates the control signals for the PGAs and the RSSI information which is readable via the bus. The AGC system is optimized for best SNR and IM performance.