SP8861NA Просмотр технического описания (PDF) - Zarlink Semiconductor Inc

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производитель

SP8861NA

1·3GHz Low Power Single-Chip Frequency Synthesiser

Zarlink Semiconductor Inc 

FROM

CHARGE

PUMP

C2

C1

R2

R1

−

+

TO VCO

FROM

CHARGE

PUMP

Cx

C1

R2

R1

−

+

SP8861

R3

TO VCO

C3

Fig. 11 Standard form of third order loop filter

Fig. 12 Modified form of third order loop filter

where Ku, K0, N and vn are as defined for the second order

loop and F0 is the phase margin, normally set to 45°. These

values can now be substituted in equation (3) to obtain a value

for C1 and in equations (4) and (5) to determine values for C2

and R2.

Example

Calculate values for a third order loop with parameters as

for the second order loop and F0 = 45°.

From

equation

(5):

t3

=

2tan 45°1cos145°

500Hz32p

= 0·4142

3161·6

∴t3 = 131·8µs

From equation (4):

t2 =

1

(500323p)231·31831024

∴t2 = 768·7µs

Using these values in equation (3):

t1 =

7·963102332p310MHz/V

1

3[A]2

80003(50032p)2

where

A

=

11vn2

11vn2

t22

t32





= 11(50032p)23(7·68731024)2

11(50032p)23(1·31831024)2

1

t1

=

500141·6  6·832

7·896110101·1714





2

= 6·3343102632·415

∴t1 = 15·3µs

Now, since t1 = C1R1 and R1 =1kΩ, C1 1=·5313013 025

∴C1 = 0·0153µF

For Fig. 11,

t2 = R2 (C11C2)

For Fig. 12,

t3 = C2R2

Substituting for C2:

t2

=

R2 C11Rt32





=

R2

C11t3

or, R2=

t22t3

C1

=

7·6873102421·31831024

0·015331026

∴R2 = 41·627kΩ

t3

=

C2R2

= t3

R2

= 1·31831024

41627

∴C2 = 3·17nF

For Fig. 12,

t1 = C1R1

or,

C1

=

1·5331025

103

∴C1 = 0·0153nF

t2 = C1R2

or,

R2

=

7·68731024

1·5331028

∴R2 = 50·242kΩ

t3 = C2R3

Since the values of C2 and R3 are independent of the other

components, either can be chosen and the other determined.

Assuming that R3 = 1kΩ, then

C2

=

1·31831024

103

∴C2 = 0·01318µF

11

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