M2050/51/52 Datasheet Rev 1.0

8 of 12

Revised 23Jun2005

Integrate d Circu it Systems, Inc. ● Communications Modules ● www.ics t.com ● tel (508) 852-5400

Integrated

Circuit

Systems, Inc.

M2050/51/52

Preliminar y In f o r m atio n

External Loop Filter

To provide stable PLL operation, the M2050/51/52

requires the use of an external loop filter. This is

provided via the provided filter pins (see Figure 5).

Due to the differential signal path design, the

implementation requires two identical complementary

RC filters as shown here.

Figure 5: External Loop Filter

PLL bandwidth is affected by the “Mfec” value and the

“Mfin” value, as well as the VCSO frequency. The

FEC_SEL

setting can be used to actively change PLL loop

bandwidth in a given application. See “Mfec and Rfec

Divider Look-Up Tables (LUTs)” on pg. 3.

See Tables 9, 10, and 11, Example External Loop Filter

Component Values, on pg. 8.

PLL Simulator Tool Available

A free PC software utility is available on the ICS website

(www.icst.com). The M2000 Timing Modules PLL

Simulator is a downloadable application that simulates

PLL jitter and wander transfer characteristics. This

enables the user to set appropriate external loop

component values in a given application.

Refer to the M2050/51/52 product web page at

www.icst.com/products/summary/m2050-2052.htm

for additional product information.

C

POST

C

POST

VC

nVC

R

POST

nOP_OUT

OP_OUT

R

POST

R

LOOP

R

LOOP

C

LOOP

C

LOOP

OP_IN

nOP_IN

6

7

5

49

8

Example External Loop Filter Component Values

for M2050-11-644.5313 and M2050-11-669.6429

Device Configuration

Example Loop Filter Component Values

Nominal Performance With Values

(MHz)

(MHz)

FIN_

FEC_

... SEL1:0

Mfin M R

Phase Det.

Freq. (MHz)

R Loop

C Loop

R Post

C Post

PLL Loop

Bandwidth

Damping

Factor

Passband

Peaking (dB)

Post Filter

Bandwidth

125.00

644.5313 0 1 0 0 5 33 32

3.9063

0.043

125.00

669.6429 0 1 1 0 5 15 14

8.9286

0.039

Table 9: Example External Loop Filter Component Values for M2050-11-644.5313 and M2050-11-669.6429

Example External Loop Filter Component Values

for M2051-11-625.0000

Device Configuration

Example Loop Filter Component Values

Nominal Performance With Values

(MHz)

(MHz)

FIN_

FEC_

...SEL1:0

Mfin M R

Phase Det.

Freq. (MHz)

R Loop

C Loop

R Post

C Post

PLL Loop

Bandwidth

Damping

Factor

Passband

Peaking (dB)

Post Filter

Bandwidth

644.5313 625.0000 1 1 0 0

32 33 19.5313

0.04

Table 10: Example External Loop Filter Component Values for M2051-11-625.0000

for M2052-11-644.5313

Device Configuration

Example Loop Filter Component Values

Nominal Performance With Values

(MHz)

(MHz)

FIN_

FEC_

...SEL1:0

Mfin M R

Phase Det.

Freq. (MHz)

R Loop

C Loop

R Post

C Post

PLL Loop

Bandwidth

Damping

Factor

Passband

Peaking (dB)

Post Filter

Bandwidth

693.4830 644.5313 1 1 0 0 1 79 85

8.1586

0.031

Table 11: Example External Loop Filter Component Values for M2052-11-644.5313

Note 1: K

Factor, and Passband Peaking. For PLL Simulator software, go to www.icst.com.