4.2. Operating Modes
The Si4734/35 operates in either an FM receive or an AM/SW/LW receive mode. In FM mode, radio signals are received on FMI (pin 2) and processed by the FM front-end circuitry. In AM/SW/LW mode, radio signals are received on AMI (pin 4) and processed by the AM front-end circuitry. In addition to the receiver mode, a clocking mode allows the Si4734/35 to be clocked from a reference clock or crystal. On the Si4735, an audio output mode is available as analog and/or digital audio output. In the analog audio output mode, pin 13 is ROUT, pin 14 is LOUT, pin 17 is GPO3. In the digital audio mode, pin 15 is DOUT, pin 16 is DFS, and pin 17 is DCLK. Concurrent analog/digital audio output mode requires pins 13, 14, 15,16, and 17. The receiver mode and the audio output mode are set by the POWER_UP command listed in Table 12. Si473x Command Summary.
4.3. FM Receiver
The Si4734/35's patented digital low-IF architecture reduces external components and eliminates the need for factory adjustments. The Si4734/35 receiver supports the worldwide FM broadcast band (76 to 108 MHz) as well as an extended FM band (64 to 76 MHz), which may include region-specific programming such as educational channels, emergency alerts, and/or television audio. An automatic gain control (AGC) circuit controls the gain of the integrated low noise amplifier (LNA) to optimize sensitivity and rejection of strong interferers. An image-reject mixer downconverts the RF signal to low-IF. The quadrature mixer output is amplified, filtered, and digitized with high resolution analog-to-digital converters (ADCs). This advanced architecture allows the Si4734/35 to perform channel selection, FM demodulation, and stereo audio processing to achieve superior performance compared to traditional analog architectures.
4.4. AM Receiver
The highly integrated Si4734/35 supports worldwide AM band reception from 520 to 1710 kHz using a digital low- IF architecture with a minimum number of external components and no manual alignment required. This digital low-IF architecture allows for high-precision filtering, offering excellent selectivity and noise suppression. The DSP also provides 9 or 10 kHz channel selection, AM demodulation, soft mute, and additional features such as adjustable channel bandwidth settings. Similar to the FM receiver, the integrated LNA and AGC optimize sensitivity and rejection of strong interferers allowing better reception of weak stations.
The Si4734/35 provides highly accurate digital AM tuning without factory adjustments. To offer maximum flexibility, the receiver supports a wide range of ferrite loop sticks from 180–450 µH. An air loop antenna is supported by using a transformer to increase the effective inductance from the air loop. Using a 1:5 turn ratio inductor, the inductance is increased by 25 times, easily supporting all typical AM air loop antennas which generally vary between 10 and 20 µH.
4.5. SW Receiver
The Si4734/35 is the first fully integrated IC to support AM and FM, as well as short wave (SW) band reception from 2.3 to 21.85 MHz fully covering the 120 meter to 13 meter bands. The Si4734/35 offers extensive shortwave features such as continuous digital tuning with minimal discrete components and no factory adjustments. Other SW features include adjustable channel step sizes in 1 kHz increments, adjustable channel bandwidth settings, advanced seek algorithm, and soft mute.
The Si4734/35 uses the FM antenna to capture short wave signals. These signals are then fed directly into the AMI pin in a wide band configuration. See “AN382: Si4734/35 Designer’s Guide” for more details.
4.6. LW Receiver
The Si4734/35 supports the long wave (LW) band from 153 to 279 kHz. The highly integrated Si4734/35 offers continuous digital tuning with minimal discrete components and no factory adjustments. The Si4734/35 also offers adjustable channel step sizes in 1 kHz increments, adjustable channel bandwidth settings, advanced seek algorithm, and soft mute.
The Si4734/35 uses a separate ferrite bar antenna to capture long wave signals.
