Filter
Top Products
Design Guide 35
5.4.4 Reference Clock Generation
A 37.5 MHz reference clock with a +/- 100 ppm accuracy is required for proper operation of the
GD31244. This is generated from an external oscillator connected directly to the XI input.
Optionally, a 37.5 MHz crystal may be connected between the XI and XO pins with a 20 pF
capacitor from XI to ground and another from XO to ground. The following are the crystal
characteristics:
• Frequency: 37.5 MHz +/- 100 ppm
• Mode: Fundamental
• Type: Parallel resonant
• ESR: 30 Ohms maximum
• Load Capacitance: 20 pF
• Shunt Capacitance: 7pF
• Drive Level: 500 mW maximum
• Recommended Vendor/Part Number: Fox Electronics, Part number: 278-37.5-8 (This is an
HC-49SD surface mountable package.)
Place the crystal near the GD31244 and isolated from noisy circuits as much as possible.