This circuit is that universal, that you always wanted to have one. Even so we integrated it in many designs, a limited meaurement range of a Microsemi Phase Noise Test Bench triggered the design of a standalone version.

This standalone prescaler is not very power-hungry (≥ 8 V, 10 mA) and the divider value may be changed by assembly / disassembly of two different resistors. (:2, :4, :8, see schematics or datasheet)

You may use it to extend the measurement range of many devices, e.g. frequency counters or to create harmonics and filter out the interesting one.

The Circuit has an input amplifier with a very high gain, as it has to deal with signals from -10 dBm up to +10 dBm. Therefore it mayst happen, that the circuit starts to oscillate, when nothing is connected at the input. If your setup always has a signal at the input, proceed to next paragraph.




We used a Resistor of 470 kΩ at the unused input to unbalance the working point of the input amplifier. After the resistor has been added, we measured a DC voltage of 3.40 V and 3.43 V. Tendency to oscillate was reduced drammatically by that. You may want to reduce the value of the resistor further, at the price of a reduced sensitivity.

As with other "handy" things, you may use them for different applications.

It is a well known secret, that the phase noise of an oscillator improves by 3 dB with every division by two. That's how you build a synthesiser powerful enough to challenge (and beat) the venerable hp 8640.

Another fact is, that a square wave (which is produced by the digital divider circuit inside) is rich in harmonics. Therefore one could synthesise a frequency by dividing a good quality crystal oscillator and filter out the desired harmonic.




Another application is the extension of the Measurement Range of a Phase Noise Test Setup or Frequeny Counter.

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Picture from D goes here :-)

The output of the Prescaler is slightly to low to be directly connected to TTL circuits. A buffer with some gain is necessary. The datasheet specifies a typical output voltage of 800 mVpp up to 350 MHz, decreasing to 450 mVpp at 550 MHz.

We usually use a Buffer made with a BFR92A (Rc = 360 Ω, Rcb = 3.6 kΩ), capacitively coupled at the input, dc coupled at the output. Supply is 5 V.


Output at 25 MHz (100 MHz : 4), as seen on a Scope

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