GS1671 datasheet(30/130 Pages) SEMTECH

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GS1671 HD/SD SDI Integrated Receiver

Data Sheet

53737 - 2

September 2012

30 of 130

4.5 External Crystal/Reference Clock

The GS1671 requires an external 27MHz reference clock for correct operation. This

reference clock is generated by connecting a crystal to the XTAL1 and XTAL2 pins of the

device. See Application Reference Design on page 124. Table 4-3 shows XTAL

characteristics.

Alternately, a 27MHz external clock source can be connected to the XTAL1 pin of the

device, as shown in Figure 4-2.

The frequency variation of the crystal including aging, supply and temperature

variation, should be less than +/-100ppm.

The equivalent series resistance (or motional resistance) should be a maximum of 50

Ω.

The external crystal is used in the frequency acquisition process. It has no impact on the

output jitter performance of the part when the part is locked to incoming data. Because

of this, the only key parameter is the frequency variation of the crystal that is stated

above.

Figure 4-2: 27MHz Clock Sources

External Crystal Connection

XTAL1

XTAL2

XTAL1

XTAL2

External Clock Source Connection

16pF

External

Clock

Notes:

1. Capacitor values listed represent the total capacitance,

including discrete capacitance and parasitic board capacitance.

2.XTAL1 serves as an input, which may alternatively accept a 27MHz clock

source.

Table 4-3: Input Clock Requirements

Parameter

Min

Typ

Max

UOM

Notes

XTAL1 Low Level Input Voltage

(Vil)

−−

20% of VDD_IO

XTAL1 High Level Input

Voltage (Vih)

80% of VDDIO

−−

XTAL1 Input Slew Rate

−−

V/ns

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