271 TT05 Analog Testmacro (Ringo, DAC)
271 : TT05 Analog Testmacro (Ringo, DAC)
- Author: Harald Pretl and Jakob Ratschenberger
- Description: For future analog enablement of TinyTapeout we designed a few simple analog blocks for testing the flow. The first block is a ca. 500kHz ring oscillator outputting a square-wave signal. The second block is a 3bit R-2R DAC outputting a programmable dc voltage. Both analog output signals can be gated or shorted using integrated transmission gates. To add a further level of madness, we have placed and routed this analog macro using an experimental automatic analog PnR tool, currently under development by the authors.
- GitHub repository
- Open in 3D viewer
- Clock: 0 Hz
- Feedback: ✅ 2
How it works
A ring oscillator (ca. 500kHz) produces a square-wave signal available at UA[0]. A 3-bit R-2R DAC produces a dc voltage availabel at UA[1].
How to test
Enable the respective blocks, and enable the transmission gates to connect the block outputs to UA[0] and UA[1], respectively. The DAC voltage can be changed by setting the digital inputs accordingly.
External hardware
scope, multimeter
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | dac_in[0] | UA[0]: Ringo output (when TG enabled) | |
| 1 | dac_in[1] | UA[1]: DAC output (when TG enabled) | |
| 2 | dac_in[2] | ||
| 3 | Enable TG for DAC output to UA[1] | ||
| 4 | |||
| 5 | Enable TG for ringo output to UA[0] | ||
| 6 | Enable ringo | ||
| 7 | Short UA[0] and UA[1] for testing |
User feedback
- mattvenn: DAC works fine, Ring oscillator is round 400kHz, so around 100kHz slower than intended
- MichaelBell: DAC works well, voltage levels look pretty accurate with a minimum of around 8mV and max of around 1.57V. Rise and fall times around 400ns, with fall a bit faster than rise. Ring oscillator gave 409kHz for me, falling to 407kHz when I put my finger on the chip to warm it up very slightly. I get ~148ns rise, ~162ns fall. Running the ring oscillator and changing the core voltage, I see 505kHz when running at 2.0V, down to around 4.3kHz at 0.8V. Below 0.8V the signal gets weaker, but at 0.6V there is still just about a signal at 41Hz!