ICS501 – Integrated PLL Clock Multiplier

Before clock multiplier circuits existed, they had to be implemented with discrete parts. This took up quite a bit time in design and prototyping. Luckily the days are over and we can use integrated clock multipliers such as the LOCO™ PLL clock multiplier ICS501.

I stumbled across a box of ICS501 PLL clock multipliers from Integrated Device Technology and a bunch of PCBs I developed for them. The project dates back a few years when I needed an easy to build small clock multiplier. The multiplier was supposed to accept a regular through-hole and put out a frequency twice the crystal frequency.

While designing that circuit, I stumbled across the ICS501. This tiny integrated circuit is extremely versatile. The IC has an inbuilt crystal oscillator, 9 different multiplication factors between 2 and 8, and promises a low jitter of 25 ps.

Possible multiplication factors between 2X and 8X. A '1' stands for logic high, a '0' for logic low, and 'M' stands for tri-state (open)

Possible multiplication factors between 2X and 8X. A ‘1’ stands for logic high, a ‘0’ for logic low, and ‘M’ stands for tri-state (open)

The IC is only available in an 8-SOIC package. Therefore, I designed the whole circuit around it with surface mount parts also.

Pin assignment of the ICS501

Pin assignment of the ICS501

The circuit is pretty straight forward: a linear voltage regulator, the ICS501, a capacitor and of course a crystal – that’s all.

Simple clock multiplier for multiplication factors between 5 - 27 MHz

Simple clock multiplier for multiplication factors between 5 – 27 MHz

Being able to multiply frequencies between 5 – 27 MHz all the way up to 160 MHz opens up new options for the use of standard off-the-shelf crystals to generate higher frequency signals. Thanks to the decimal factors, we can now even achieve output frequencies which would have been impossible to generate from the same crystal frequency with discrete multipliers.

For instance, with a 23.16 MHz crystal, a multiplication factor of 6.25 and a small antenna on the output pin, we get an extremely simple 144.75 MHz 2m-band VHF tracking device suitable for direction finding exercises. The small device can even be modulated (FM) if we use a variable capacitance diode (varicap) instead of the trimmer capacitor and we inject a modulation signal.

Links and Sources:
[1] ICS501 Datasheet ICS501 Datasheet

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