AK8186B Datasheet, PDF (24/69 Pages) Asahi Kasei Microsystems – Multi Output Clock Generator with Integrated 2.0GHz VCO

AK8186B
External VCO/VCXO
The AK8186B supports an external VCO/VCXO. The CLK/CLK input can be used as a differential feedback
for an external VCO/VCXO. The input frequency is up to 500MHz.
PLL EXTERNAL LOOP FILTER
The loop filter supplies a voltage to the VCO via the LF pin to move the VCO frequency up or down. When
using the internal VCO, the external loop filter should be referenced to the BYPASS pin for optimal noise
and spurious performance. An example is shown in Fig.13. The values of loop filter must be calculated for
each PLL. It depends on the VCO frequency, the Kvco, the PFD frequency, the CP current, the desired loop
bandwidth and the desired phase margin.
Figure 12 Example of External Loop Filter for the Internal VCO
Figure 13 Example of External Loop Filter for an External VCO
FEEDBACK DIVIDER (N DIVIDER)
The N divider consists of a prescaler (P), A and B counters.
Figure 14. N divider
PRESCALER
The prescaler is a dual modulus counter which has two modes of operation. Division value of A counter
defines the mode as below.
1) When A = 0: a fixed divide (FD) mode where the prescaler divides by P.
2) When A  0: dual modulus (DM) mode where the prescaler divides by P and (P+1).
Sep-2012
- 24 -
draft-E-02