TDA7706 Datasheet, PDF (10/16 Pages) STMicroelectronics – Highly integrated tuner for AM/FM car-radio

Function description
TDA7706
2.6
IF A/D converters
A high performance IQ-IFADC converts the IF signal to the digital domain for subsequent
digital signal processing.
Two fully differential, continuous-time Sigma-Delta () IF-ADCs are used for both the'I' path
and the 'Q' path. For each IFADC, two fully differential input nodes are fed with an input
signal having a bandwidth up to 325 kHz. This fully differential design provides good
suppression of even-order harmonics. For complex filtering, the input signals of the 'I' path
and the 'Q' path have a 90 degree phase shift. The IFADC sampling frequency is 36.48
MHz.
2.7
Audio D/A converters
A CD-quality (>100dB DR) stereo DAC provides the left/right audio signals after IF
processing and stereo-decoding by the DSP. In presence of an external HD Radio decoder
the DAC outputs the high quality audio resulting from the decoding of the HD Radio
transmissions.
2.8
VCO
The VCO is fully integrated without any external tuning component. It covers all the FM
frequency bands including EU, US, Japan, East-Europe, Weather-Band and the AM-bands
including LW, MW and SW. Its center frequency is approximately 2.7 GHz.
2.9
2.9.1
PLL
Tuner PLL
The very high-speed tuning PLL is able to settle within about 100 µs for fast RDS
applications. The frequency step can be as low as 5 kHz in FM and 500 Hz in AM.
2.10
Crystal oscillator
The device works with a 36.48 MHz fundamental tone crystal. The oscillator block diagram
is shown in Figure 3. On the PCB the crystal must be connected as close as possible to the
chip oscillator input and output pins of the chip. The internal load capacitance together with
pin and pad capacitance is optimized for fundamental tone crystal units at 36.48MHz. It is
not recommended to put any additional external load capacitors. By suitably configuring pin
#9 (CK_SEL), the device can be operated as either a clock master or a clock slave. If pin 9
is left open or tied to GND, the device is configured as clock master (typical operation
mode). In case the device is configured as clock slave, pin 9 needs to be connected to 5V.
Then the crystal oscillator is switched off and the device expects a crystal equivalent signal
on the OSCout/OSCin pins.
10/16
Doc ID 022898 Rev 3