Frequency Synthesizer 频率合成器

lin258437570

The MT612X includes a frequency synthesizer with a fully integrated RF VCO to generate RoX and TX local oscillator
frequencies. The PLL locks the RF VCO to a precision reference frequency at 26 MHz. In order to reduce the inherent
spur caused by fractional-N synthesizers, a 3rd-order sigma-delta modulator with dithering  fufnction is used to generate
the prescaler divider number N. The prescaler is based on a multi-modulus architecture with programmable divider
e
numbers ranging from 64 to 127. A conventional digital-type PFD with a charge pump is used for phase comparison in
the PLL. By changing the output current of the charge pump, the phase detectors gain can be programmed from75/π
μA/rad to 600/π μA/rad.
a
To reduce the acquisition time or to enable fast settling time for multi-slot data services such as GPRS, a digital loop
(calibration loop) along with a fast-acquisition system are implemented in the synthesizer. Once the synthesizer is
programmed, the RF VCO is pre-set to the vicinity of the desired freqlueency by a digital calibration loop. After the
calibration, a fast-acquisition system is utilized for a period of time to faecilitate fast locking. Once the acquisition is done,
the PLL reverts back to the normal operation mode.
该mt612x包括一个频率合成器与一个完全整合的射频压控振荡器产生rox和TX的本地振荡器
频率。锁相环锁定射频压控振荡器，以精确的参考频率在26兆赫。 ，以减少内在
刺激所造成的N分数合成，第三阶Σ - Δ调制器与抖动fufnction是用来产生
该分频器分频器人数12月31日该分频器是基于多模架构与可编程分压器
e
人数不等，从64至127 。传统的数字型维和筹资处与电荷泵是用于第一阶段的比较
锁相环。通过改变输出电流电荷泵，第二阶段探测器增益可以编程from75 / π
μ /拉德，以600 / π μ /拉德。
字母a
以减少采集时间或使快速解决的时间多插槽的数据服务，如GPRS的，数字环路
（校准回路）随着一个快速采集系统的实施，在合成器。一旦合成器是
编程，射频压控振荡器是预先设定的，以附近的理想freqlueency由一个数字校准循环。后
标定，快速采集系统是用于在一段时间内，以faecilitate快速锁定。一旦收购完成后，
锁相环还原到正常的运作模式。
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