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9.4 Spice Simulations

More detailed analysis of the GS9035C PLL can be done

using SPICE. A SPICE model of the PLL is shown below:

Fig. 16 SPICE Model of PLL

The model consists of a voltage controlled current source

voltage controlled voltage source (E1), and a voltage

source (V1). R2 is necessary to create a DC path to ground

for Node 1.

V1 is used to generate the input phase waveform. G1

compares the input and output phase waveforms and

generates the charge pump current,

components integrate the charge pump current to establish

the loop filter voltage. E1 creates the output phase

waveform (PHIO) by multiplying the loop filter voltage by

The netlist for the model is given below. The .PARAM

statements are used to set values for

Figure 15.

SPICE NETLIST * GS9035C PLL Model

.PARAM ICP = 165E-6 KF= 90E+6

.PARAM N = 1 D = 0.5

.PARAM PI = 3.14

.IC V(Phio) = 0

.ac dec 30 1k 10meg

RLF 1 LF 1000

CLF1 1 0 15n

CLF2 0 LF 15p

E_LAPLACE1 Phio 0 LAPLACE {V(LF)} {(2*PI*KF)/(N*s)}

G1 0 LF VALUE{D * ICP/(2*pi)*V(Phii, Phio)}

V1 2 0 DC 0V AC 1V

R2 0 1 1g

.END

10. I/O DESCRIPTION

10.1 High Speed Inputs (DDI/DDI)

DDI/DDI

are

high

impedance

inputs

which

accept

differential or single-ended input drive. Two conditions must

be observed when interfacing to these inputs:

1. Input signal amplitudes are between 200 and 2000mV

2. The common mode input voltage range is as specified

in the DC Characteristics table.

Commonly

used

interface

examples

are

shown

in

Figures 17 and 18.

Figure 18 illustrates the simplest interface to the GS9035C.

In this example, the driving device generates the PECL

level signals (800mV amplitudes) having a common mode

input range between 0.4 and 4.6V. This scheme is

recommended when the trace lengths are less than 1in. The

Ground), depends on the output driver circuitry of the

previous device.

Fig. 17 Simple Interface to the GS9035C

0

50

100

150

200

250

300

350

400

0

200

400

600

800

1000

1200

1400 1600

1800

PHII

PHIO

R2

E1

G1

V1

2

IN+

IN-

1

LF

NOTE: PHII, PHIO, LF and 1 are node names in the SPICE netlist.

DDI

DDI

GS9035C