GS2971 Datasheet, PDF (34/148 Pages) Semtech Corporation – 3Gb/s, HD, SD SDI Receiver, with Integrated Adaptive Cable Equalizer complete with SMPTE Audio and Video Processing

4.6 External Crystal/Reference Clock
The GS2971 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 142. 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 4-4.
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 50Ω.
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.
External Crystal Connection
16pF
K6 _XTAL1
External Clock Source Connection
External
Clock
K6 _XTAL1
16pF
J6 _XTAL2
NC
J6 _XTAL2
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.
Figure 4-4: 27MHz Clock Sources
Table 4-3: Input Clock Requirements
Parameter
Min
Typ
XTAL1 Low Level Input Voltage
−
−
(V_il)
XTAL1 High Level Input
80% of VDDIO
−
Voltage (V_ih)
Max
20% of VDD_IO
−
UOM
V
V
Notes
3
3
GS2971 3Gb/s, HD, SD SDI Receiver
Data Sheet
45898 - 2
September 2012
34 of 148