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In a previous post we described Power Supply Rejection Ratio (PSRR) and discussed the ways it can impact an oscillators performance. In this update one of the ways we approach measuring PSRR on our devices. Continue reading
What is PSRR?
Power Supply Rejection Ratio or Power Supply Ripple Rejection (PSRR) is a measure of how well a circuit rejects noise, of various frequencies, injected at its voltage input. The ripple can be induced from a number of sources, such as a 50Hz/60Hz supply ripple, a switching ripple from a DC/DC converter, or a ripple due to the sharing of an input supply between different circuit blocks on the board. In the timing solutions world, when discussing PSRR we are typically referring to supply ripple.
A common VCXO specification is the Vc input impedance. A typical value might be 100KOhm or 10MegOhm. What does this actually mean?
Like most oscillators, VCXOs have many specifications. APR – Absolute Pull Range – is a single specification that combines many of them to make selection easy. The term “Pull” is unique to the oscillator industry and refers to the small frequency tuning available via the voltage control pin. Pull is measured as df/fnom in ppm.
TCXO: Stability vs Accuracy
Temperature compensated crystal oscillators (TCXOs) are used for frequency reference in systems that require a frequency stability of 10 ppm or better, which typically cannot be achieved by a standard XO (crystal oscillator) or VCXO (voltage controlled crystal oscillator).