Building a Sweep Generator for BK 4011

Posted on Feb 5, 2014

A teardown of a BK Precision 4011 5MHz function generator a few weeks ago. Like most of basic function generators in old days, BK 4011 does not offer frequency sweep as an option. What it does include is a VCG (Voltage controlled Generator) input, which essentially is just a VCO and it can be used in conjunction with an external sweep genera

Building a Sweep Generator for BK 4011
Click here to download the full size of the above Circuit.

tor to generate frequency sweeps. In this post I will show you a simple sweep generator I built. It can be used to generate both the sweep waveform and synchronization signal needed for any function generator that has a VCG/VCO input. The sweep frequency can be adjusted from under a Hertz to several kHz. The sweep waveform can be switched between linear and logrithm modes and can be easily extended to accommodate other arbitrary waveforms. At the core of this sweep generator lies an 8-bit parallel-input DAC DAC0800. This digital to analog converter is driven by an MCU (Atmega328P) which generates the sweep waveform. The reason that I used a parallel DAC in this situation is for its speed. While DAC0800 is a rather old chip, it can operate at a relatively fast speed which makes it suitable for waveform generation use. It is also very inexpensive and easy to use. Modern DACs using serial protocols (e. g. SPI/I2C) on the other hand, can cost significantly more for the same operation speed. One draw back of using DAC0800 is that it requires dual supply rails for operation. While there are ways ( TI AN-1525 ) to use DAC0800 with a single supply, they add quite a bit of complexity to the circuit design. So to keep everything simple, I followed the dual supply route. To provide the negative voltage required by DAC0800 I used Maxim`s MAX889 inverting charge pump. Because BK 4011 ²s VCG input range is 0-10V, the output from DAC0800...

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