6 GHz RF Signal Generator


Every once in a while I need an RF frequency generator. Nothing fancy, but something that can create a signal at a much higher frequency than my DDS signal generator is capable of.

Linear Technology released a very interesting part, the LTC6946. This is an RF PLL synthesizer with an integrated VCO. Basically, you give it a reference input signal, you program the internal PLL registers with your desired divide ratios, and it generates the output signal. There are 3 versions of the IC available, and depending upon which one you choose you can get an output range between 373 MHz and 5.79 GHz. I selected the LTC6946-3, the highest frequency member of the family, which provides an output range of 640 MHz to 5.79 GHz, almost 6 GHz, with a hole between 2.85 – 3.6 GHz.

To provide a way for the user to select the frequency, I used a Texas Instruments Cortex M3 development board. This has their Stellaris ARM Cortex-M3 processor connected to a 3.5” touch-screen colour LCD. An application for this board allows the user to enter their desired frequency, calculates the necessary “magic numbers” for the LTC6946 PLL registers, and then programs the LTC6946 via its SPI port. It looks very pretty – far nicer than the DDS does. The following pages provide full hardware and software information (including software source code) for this project.