DS_S1M8837 Datasheet, PDF (12/29 Pages) Samsung semiconductor – FRACTIONAL-N RF/INTEGER-N IF DUAL PLL

S1M8836/37
FRACTIONAL-N RF/INTEGER-N IF DUAL PLL
When the PLL is in the locked state, the RF VCO's frequency will be N_INT + N_FRAC times the comparison
frequency, where N_INT is the integer divide ratio and N_FRAC is the fractional component.
The S1M8836/37 has new improved features compared to conventional Integer-N PLLs.
The fractional-N PLL is available for the RF. The fractional synthesis frequency as is AMPS and IS-95A/B/C.
This makes it possible to widen the loop bandwidth as wide as 20kHz or wider for a faster lock-up time and to
improve the in-band phase noise performance due to the reduced divide ratio N. Such S1M8836/37 in the
fractional-N mode is suitable for CDMA, GSM and PCS band applications.
Also, from the programmability of the charge pump, the users can easily design a stable loop by free selection of
loop components and reach to the low spurious, the low power PLL by an optimized current selection.
Prescaler
The RF/IF prescaler consists of a differential input buffer and ECL frequency dividers. The input buffer amplifies
the input signal from the external VCO to the required level set by sensitivity requirements. The output of the
amplifier delivers a differential signal to the divider with the correct DC level. The buffer may be either single-
ended or differentially driven. The single-ended operation is preferred in typical applications due to external VCO.
In this case, we recommend that the complementary input /fin of the input buffer be AC coupled to ground
through external capacitors, even though it is internally coupled to ground via an internal 10pF capacitor. The
other input pin fin of the buffer also needs external capacitor for decoupling the DC component and controlling
the input power level.
The RF prescalers of S1M8836 and S1M8837 provide 8/9/12/13 and 16/17/20/21 prescaler ratio, respectively.
The IF prescaler of S1M8836/37 contains 8/9 dual modulus prescaler.
Reference Oscillator Inputs
The reference oscillator frequency is provided by an external reference such as TCXO through the OSC_in.
It drives both the IF R and RF R counters.
Programmable Dividers (RF/IF N Counters)
The RF N counter can be configured as a fractional counter. The fractional-N counter is selected when the
Frac-N_SEL bit becomes HIGH.
In the fractional mode, the S1M8836 is capable of offering a continuous integer divide range from 25 to 1023 and
the S1M8837 offering a continuous integer divide range from 49 to 2047.
The S1M8836/37 IF N counter supports an integer counter mode only, not including fractional counter, and is
capable of operating from 45MHz to 520MHz offering a continuous integer divide range from 72 to 32767.
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