Precision Low-Voltage Function Generator

[jram112]

I'm wanting to create a precision low-voltage function generator with isolated power supply. I only need sine and square waves with amplitudes between 10uV - 1V and frequency range between 0.1Hz-10kHz. This device will be used to calibrate biomedical hardware. It will also include differential and single ended outputs.

This device is very similar to what I need, but is almost 600 USD: http://www.ecgsimulators.com/products/model-220-function-generator. I think I'd rather create one and share the design with everyone. However, I have aquired one of these for $75 and will be performing a Dave Jones' inspired tear down with my screwdriver and camera...."take it apart".

My initial thoughts are to use a DDS chip like Analog Device's AD9800 series DDS >> then condition the signal with a LPF >> then use a precision single-chip voltage divider network to get lower voltages >> finally followed with a precision auto-zeroing opamps for buffering. Amplitudes will be controlled by the DDS chip output.

This may be a horrible initial design, but that's why I need input from you guys. How would you guys design such a device?

[fcb]

Use an audio DAC.

[dannyf]

My initial thoughts are to use a DDS chip like Analog Device's AD9800 series DDS >> then condition the signal with a LPF >> then use a precision single-chip voltage divider network to get lower voltages >> finally followed with a precision auto-zeroing opamps for buffering.

Up until the opamp part, that's what those $5 ebay DDS modules do.

Amplitudes will be controlled by the DDS chip output.

The stock ebay dds module allows amplitude modulation via a small change, but probably not at your resolution / precision. A better approach would be to use an outboard pga. The 10uv-1v range is actually pretty wide and you may want to look into an analog pga rather than a digital one.