commit | 1136fcf31d38eb763a861336fa28bad9d72c825e | [log] [tgz] |
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author | chrische <christoph-weiser@gmx.de> | Fri Jul 22 21:28:05 2022 +0200 |
committer | chrische <christoph-weiser@gmx.de> | Fri Jul 22 21:28:05 2022 +0200 |
tree | e0434c02b811c79d1cc7f034f39c31ec5ad587c7 |
added content
This submission features:
Many detailed improvement to the previous mpw6 submission.
Critical bugfixes related to connection issues on top-level.
The first open source 10 bit SAR-ADC
Bandgap reference.
Testbuffer with multiplexer input.
Clock generator
2 linear regulators, 1.2V and 1.5V.
Bias current/voltage generator.
Included are:
Simply source cadrc in the xschem folder and execute xschem afterwards to get an full overview.
The layout was created using magic with the open_pdk sky130 setup as a pcell generator and klayout for the layout and assembly of the gds.
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The ADC is a differential 10 bit SAR, with a capacitative DAC.
Parameter | Min | Typ | Max | Unit |
---|---|---|---|---|
$A_{VDD}$ | 1.8 | V | ||
$D_{VDD}$ | 1.8 | V | ||
$V_{in,p}$ | $A_{VSS}$ | $A_{VDD}$* | V | |
$V_{in,n}$ | $A_{VSS}$ | $A_{VDD}$* | V | |
$V_{CM}$ | $A_{VDD}$/2 | V | ||
Resolution | 10 | bits | ||
$f_{clk}$ | 10 | MHz | ||
$T_{A}$ | -20 | 85 | °C | |
Area | 0.08745 | mm² | ||
$C_{in}$ | 3 | pF |
* 3.3V if ADC is not sampling the input signal.
The Architecture of SAR is shown below. It is a differential architecture with a top-plate sampled CDAC.
The comparator is pretty standard single stage topology. It features a trim array to calibrate its input offset.
The entire control logic is synthesized using the openlane flow. This allows to easily integrate the trim logic for the comparator into the overall control logic block.
For faster simulation the ngspice mixed-mode xspice feature was used. Yosys can be used to synthesize a xspice compatible netlist that only uses code-model components (NAND, NOT, DFF etc.) which speeds up simulation substantially.
The DAC is a capacitative DAC made from a total of 1024 unit caps per side.
The unit size of the DAC elements is ~3fF based on FEM simulation carried out with Elmer FEM. You can find the full simulation setup in the elmer subfolder of this repo.
The process is:
The DAC is top-plate sampled using a bootstrapped switch.
The complete SAR-ADC layout can be seen below. It occupies an area of approximately 0.08745 mm² (530 μm x 165 μm).
The result of a input voltage sweep across the full input range (-1.8V to 1.8V) can be seen below.
The main section contains various blocks that support the independent operation of the ADC.
The complete Main layout can be seen below. It occupies an area of approximately 0.1054 mm² ( 285 μm x 370 μm).