ICS8735-21 datasheet(10/20 Pages) IDT

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ICS8735-21

700MHZ, DIFFERENTIAL-TO-3.3V LVPECL ZERO DELAY CLOCK GENERATOR

IDT™ / ICS™ 3.3V LVPECL ZERO DELAY CLOCK GENERATOR

ICS8735AM-21 REV. A JULY 31, 2008

Power Supply Filtering Technique

As in any high speed analog circuitry, the power supply pins are

vulnerable to random noise. To achieve optimum jitter perform-

ance, power supply isolation is required. The ICS8735-21 provides

separate power supplies to isolate any high switching noise from

the outputs to the internal PLL. VCC, VCCA and VCCO should be

individually connected to the power supply plane through vias, and

0.01µF bypass capacitors should be used for each pin. Figure 1

illustrates this for a generic VCC pin and also shows that VCCA

requires that an additional 10

Ω resistor along with a 10µF bypass

capacitor be connected to the VCCA pin. The 10Ω resistor can also

be replaced by a ferrite bead.

Figure 1. Power Supply Filtering

Wiring the Differential Input to Accept Single Ended Levels

Figure 2 shows how the differential input can be wired to accept

single ended levels. The reference voltage V_REF = VCC/2 is

generated by the bias resistors R1, R2 and C1. This bias circuit

should be located as close as possible to the input pin. The ratio of

R1 and R2 might need to be adjusted to position the V_REF in the

center of the input voltage swing. For example, if the input clock

swing is only 2.5V and VCC = 3.3V, V_REF should be 1.25V and

R2/R1 = 0.609.

Figure 2. Single-Ended Signal Driving Differential Input

VCC

VCCA

3.3V

Ω

10µF

.01µF

V_REF

Single Ended Clock Input

VCC

CLK

nCLK

0.1u

ICS8735-21 Datasheet(PDF) 10 Page - Integrated Device Technology