In part one, I compared the different Analog to Digital Converters (ADC) and the roles and properties of Delta Sigma ADC’s. I covered a lot of the theory behind these devices, so in this installment, I set out to find a design or two that would help me demonstrate the important points like oversampling, noise shaping and the relationship between the signal-to-noise ratio and resolution.
Check out part one to see the block diagrams of what what got us to here. The schematics shown below are of a couple of implementations that I played with depicting a single-order and a dual-order Delta Sigma modulators.
Basically I used a clock enabled, high speed comparator, with two polarities in case I got it the logic backwards in my current state of burn out to grey matter ratio. The video includes the actual schematic used.
Since I wasn’t designing for production I accepted the need for three voltages since my bench supply was capable of providing them and this widget is destined for the drawer with the other widgets made for just a few minutes of video time anyway. Continue reading “Tearing Into Delta Sigma ADCs Part 2”→
It’s not surprising that Analog to Digital Converters (ADC’s) now employ several techniques to accomplish higher speeds and resolutions than their simpler counterparts. Enter the Delta-Sigma (Δ∑) ADC which combines a couple of techniques including oversampling, noise shaping and digital filtering. That’s not to say that you need several chips to accomplish this, these days single chip Delta-Sigma ADCs and very small and available for a few dollars. Sometimes they are called Sigma-Delta (∑Δ) just to confuse things, a measure I applaud as there aren’t enough sources of confusion in the engineering world already.
I’m making this a two-parter. I will be talking about some theory and show the builds that demonstrate Delta-Sigma properties and when you might want to use them.
[Jeri] has had a bear of a time moving up to Valve Software, but electron microscope is safely in her garage (!) and her electronics lab is slowly taking shape. Since she can’t bring out the real-life gravity gun she’s working on, she decided to show off a one-bit ADC that uses just a flip-flop to sample an analog waveform into digital data.
By toggling the clock input of a 74xx74 (or any flip-flop, really) and feeding the complimentary output to back into the data input, [Jeri] can get an output that is a 50% duty cycle feeding into the input of the chip. Adding an audio input to this data input with 10k pot to this feedback loop will cause the duty cycle to change in relation to the analog input, making a one-bit ADC.
As with any electronic shortcut, there are a few drawbacks: the clock cycle feeding into the flip-flop has to be pretty fast; at least a few dozen kilohertz if you’re sampling audio. Still, if you don’t have a free ADC pin, or you’d just like to build a bitcrushing guitar pedal, it’s a very simple (and cheap) way to get analog into a digital micro.