4KHz-170MHz Wide Band RF Signal Generator I

Posted on Feb 5, 2014

While most commercial grade signal generators offer more than just outputting a sinusoidal waveform, they are quite pricey for casual use. In this article, I will show you a simple wide band signal generator that is built around a Linear Technology`s LTC6905 Silicon Oscillator, which is can generate frequencies from roughly 17MHz to 170MHz.

4KHz-170MHz Wide Band RF Signal Generator I
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Along with a FairChild Semiconductor`s 74VHC4040 12-stage high speed binary counter, this signal generator is capable of generating precise frequencies from as low as 4KHz all the way through the ranges of LTC6905. The output waveform is either square wave (via the output from 74VHC4040) or sinusoidal wave (via LTC6905 ²s output), but should be sufficient for using as reference signals. The frequency of the LTC6905 output is determined by the divider (pin 4) setting along with the voltage applied on pin 3. To generate more stable and accurate output, I used an Analog Devices` AD5235 1024 position digital potentiometer for the frequency adjustment. In general, digital potentiometer of at least 8 bits resolution is desired (AD5235 has a 10bit resolution) since we can get closer output frequency steps. To further automate the frequency range selection of LTC6905 (the frequency ranges are selected via the settings of the divider pin), I used a reed relay switch along with a Texas Instrument`s TS5A23159 low on-resistance analog switch to control the transitions among the three divider settings LTC6905 has to obtain a full range of the available frequencies continuously. The frequency transition is controlled by a switch (SW1) along with an ATmega328p MCU. In order to provide frequency ranges below LTC6905 ²s lower range (17MHz), I used a 74VHC4040 high speed 12-stage binary counter as a frequency divider so frequencies of [f_n...

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