Clock Generator Basics and Applications

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signal generator
clock signal
rf transceiver
frequency

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

clock generator

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):

SpecificationFeature supported
Input frequency rangeDifferential: 10 MHz to 750 MHz LVCMOS: 10 MHz to 250 MHz
Output frequency rangeDifferential: 480 kHz to 1.47456 GHz LVCMOS: 480 kHz to 250 MHz
Phase noise-159 dBc/Hz
Spurious-103 dBc (Max.)
Serial interfaceI2C, SPI

Clock Generator Manufacturers or Vendors

The following are popular clock generator manufacturers/vendors:

  1. Integrated Device Technology, Inc.
  2. ON Semiconductor
  3. Texas Instruments
  4. Silicon Labs (www.silabs.com)
  5. Analog Devices
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spectrum analyzer
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