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| 型号： | ATR4256-TKSY |
| 厂商： | Atmel |
| 文件页数： | 3/21页 |
| 文件大小： | 0K |
| 描述： | IC FREQ SYNTH RADIO TUNER 20SSOP |
| 产品变化通告： | ATR425x Obsolescence 03/Apr/2012 |
| 标准包装： | 830 |
| 功能： | 频率合成器 |
| RF 型： | 广播无线电 |
| 次要属性： | 缓冲输出 |
| 封装/外壳： | 20-SOIC（0.209"，5.30mm 宽） |
| 包装： | 管件 |
ATR4256
3. Functional Description
For a tuned FM-broadcast receiver, the following parts are needed:
? Voltage-controlled Oscillator (VCO)
? Antenna Amplifier Tuned Circuit
? RF Amplifier Tuned Circuit
Typical modern receivers with electronic tuning are tuned to the desired FM frequency by the
frequency synthesizer IC ATR4256. The special design allows the user to build software-con-
trolled tuner alignment systems. Two programmable DACs (Digital-to-Analog Converter) support
the computer-controlled alignment. The output of the PLL is a tuning voltage which is connected
to the VCO of the receiver IC. The output of the VCO is equal to the desired station frequency
plus the IF (10.7 MHz). The RF and the oscillator signal (VCO) are both input to the mixer that
translates the desired FM-channel signal to the fixed IF signal. For FM, the double-conversion
system of the receiver requires exactly 10.7 MHz for the first IF frequency, which determines the
center frequency of the software-controlled integrated second IF filter.
If this oscillator tuning feature is not used, the internal capacitors have to be switched off and the
oscillator has to be operated with high-quality external capacitors to ensure that the operational
frequency is exactly 10.250 MHz.
When dimensioning the oscillator circuit, it is important that the additional capacitors enable the
oscillator to operate through its complete tracking range. The oscillating ability depends very
strongly on the used crystal oscillator. Initializing the oscillator should be established without
switching any additional capacitors to guarantee that the oscillator starts to operate properly.
Due to the lower quality of the integrated capacitors compared to discrete capacitors, the
amount of the switched integrated capacitors should always be minimized. (If necessary reduce
tracking range or use a different crystal oscillator.)
The ATR4256 has a very fast response time of maximum 800 μs (at 2 mA, f Step = 50 kHz, mea-
sured on the MPX signal). It has a high signal to noise ratio. Only one supply voltage is
necessary, due to an integrated band gap.
3
4867D–AUDR–01/08
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