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====== Precise frequency and clock signal generator GPSDO01A ======

This design is focused to generating precise frequency signal with good long term stability for laboratory use. (As frequency and time normal GPS satellite clocks are used)
This design is bypass product of developing [[en:rmds]] and [[cs:acounter|Atomic counter]].

{{ :cs:designs:tools:gpsdo_prototype.jpg?400 |GPSDO01A prototype}}

The output frequency can be stabilized anywhere in 10-810 MHz range.

===== Device construction =====

{{ :cs:designs:tools:gpsdo_system.png?500 |GPSDO01A block schematics}}

Device consist following modules:

* [[cs:clkgen]]
  * [[cs:clkhub]]
  * [[en:clkdiv]]
  * [[cs:ttlpecl]]
  * [[cs:gps]]
  * [[cs:pic16f87xtq44]]
  * [[cs:usbi2c]]

===== Function principle =====

Source of high frequency signal is free-running oscillator Si570 in module [[en:clkgen|CLKGEN01B]]. This module is connected to divider [[en:clkdiv|CLKDIV01A]] and  PIC16F887 MCU, which measures frequency of this oscillator. 
Interval of measurement is variable. Basic measurement calculates with  one second τ interval. (period of [[cs:gps|GPS01A]] PPS signal can be adjusted. Thus frequency measurement can be averaged over period in fraction of seconds or tens of seconds for long term stability measurement.)

Measured data are stored in MCU memory and can be read by I²C interface. This is usually operated by host computer which computes frequency correction and apply a new frequency to si570 chip oscillator.

Frequency correction method is in principle software defined and AVAR characteristics of this frequency generator system can be adjusted to meet application requirements.

===== Related pages =====

* [[cs:time_sync]]
  * [[cs:time_interval_counter]]

===== References =====

* [[http://en.wikipedia.org/wiki/GPS_disciplined_oscillator|GPS disciplined oscillator]]
  * [[http://www.febo.com/pages/stability/|Oscillator stability]]

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