SPICE NETLIST * GS9035A 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
be in a symmetric arrangement and same physical
transmission line dimensions since common-mode signals
or common-mode noise is not terminated. In addition,
series resistors, RSOURCE, can be placed near the driving
chip to serve as source terminations. They should be equal
to the value of the trace impedance. Assuming 800mV
output swings at the driver, RLOAD =100Ω, RSOURCE =50Ω
and ZO = 50Ω.
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
R
SOURCE
SOURCE
Z
O
DDI
DDI
R
GS9035A
LOAD
R
Z
O
Fig. 20 Recommended Interface for Differential Signals
I/O DESCRIPTION
Figure 21 shows the recommended interface when the
GS9035A is driven single-endedly. In this case, the input
must be AC-coupled and a matching resistor (ZO) must be
used.
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:
DDI
1. Input signal amplitudes are between 200 and 2000mV
Z
GS9035A
O
DDI
2. The common mode input voltage range is as specified
in the DC Characteristics table.
Commonly used interface examples are shown in
Figures 19 and 20.
Fig. 21 Recommended Interface for Single-Ended Driver
High Speed Outputs (SDO/SDO and SCO/SCO)
Figure 19 illustrates the simplest interface to the GS9035A.
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
value of the resistors and the DC connection (VCC or
Ground), depends on the output driver circuitry of the
previous device.
SDO/SDO and SCO/SCO are current mode outputs that
require external pullups (see Figure 22). Note that no
external pull-ups are required when used with the GS9020.
The output signal swings are 800mV when 75Ω resistors are
used. A diode can be placed between VCC and the pullups
to shift the signal levels down by approximately 0.7 volts.
When the output traces are longer than 1in, controlled
impedance traces should be used. The pullup resistors
should be placed at the end of the output traces as they
terminate the trace in its characteristic impedance (75Ω).
V
or GND
CC
V
CC
DDI
DDI
GS9035A
75Ω
75Ω
75Ω
75Ω
SDO
SDO
V
or GND
CC
GS9035A
SCO
SCO
Fig. 19 Simple Interface to the GS9035A
When trace lengths become greater than 1in, controlled
impedance traces should be used. The recommended
interface for differential signals is shown in Figure 20. In this
case, a parallel resistor (RLOAD) is placed near the GS9035A
inputs to terminate the controlled impedance trace. The
value of RLOAD should be twice the value of the
characteristic impedance of the trace. Both traces should
V
CC
Fig. 22 High Speed Outputs with External Pullups
12
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