Clock Generator Basics and Applications
Advertisement
This page covers clock generator basics, including an application note for programmable clock signal generators and a list of clock signal generator manufacturers or vendors. Many digital circuits require a clock signal, which is a periodic square wave at a controlled frequency. The circuit that generates this clock signal is called a clock signal generator.
There are two main types of clock generators:
- Fixed: Generates a clock signal at a fixed frequency.
- Programmable (or Variable): Generates clock signals with varied input and output frequencies.
Clock signal generators have many applications, including:
- Wireless base stations for LTE, LTE-Advanced, etc.
- Picocells, femtocells, and small cells
- Sampling clocks for ADCs and DACs
- 1 Gigabit and 10 Gigabit Ethernet
- FPGA and processor clocks
- Line cards used in telephone exchanges
- Fiber Channel
- PCI Express cards
Programmable Clock Signal Generator Application Note
Figure 1: Clock generator from Silicon Labs (Si5380) used as a programmable clock signal generator in base station design.
As shown in Figure 1, the clock generator (e.g., Silicon Labs Si5380) provides a sampling clock as input to an ADC and DAC. It also provides a reference frequency signal as input to a synthesizer, which is used to provide the conversion frequency signal for RF up-conversion and down-conversion.
This clock generator boasts very low phase noise and excellent jitter performance.
The following table outlines the key features of the Silicon Labs clock generator (part number: Si5380):
Specification | Feature supported |
---|---|
Input frequency range | Differential: 10 MHz to 750 MHz LVCMOS: 10 MHz to 250 MHz |
Output frequency range | Differential: 480 kHz to 1.47456 GHz LVCMOS: 480 kHz to 250 MHz |
Phase noise | -159 dBc/Hz |
Spurious | -103 dBc (Max.) |
Serial interface | I2C, SPI |
Clock Generator Manufacturers or Vendors
The following are popular clock generator manufacturers/vendors:
- Integrated Device Technology, Inc.
- ON Semiconductor
- Texas Instruments
- Silicon Labs (www.silabs.com)
- Analog Devices