This test chip contains a first version of an SRAM block with the in development single port SRAM compiler. At the time the compiler can only generate a block with 512 words and a column demultiplexer of 4 and there has to be exactly one we bit per 8 bits in each word. For this tape-out a 512x8 block with one we pin has been used.
Current version of the SRAM cell is DRC compliant and not minimal area yet.
The top design consists of connecting in and out each of the SRAM signals using the caravan analog frame. It has the following pin mapping:
| caravan pin | signal |
|---|---|
| io_analog[4] | SRAM vdd |
| io_analog[5] | SRAM vss |
| vssd1 | logic vss |
| vccd1 | logic vdd |
| io_in[0] | SRAM we |
| io_out[1] | SRAM q[1] |
| io_out[2] | SRAM q[2] |
| io_in[3] | SRAM d[2] |
| io_in[4] | SRAM d[3] |
| io_out[5] | SRAM q[3] |
| io_out[6] | SRAM q[4] |
| io_in[7] | SRAM d[4] |
| io_in[8] | SRAM d[5] |
| io_out[9] | SRAM q[5] |
| io_out[10] | SRAM q[6] |
| io_in[11] | SRAM d[6] |
| io_in[12] | SRAM d[7] |
| io_out[13] | SRAM q[7] |
| io_in[14] | SRAM a[0] |
| io_in[15] | SRAM a[1] |
| io_in[16] | SRAM a[2] |
| io_in[17] | SRAM a[3] |
| io_in[18] | SRAM a[4] |
| io_in[19] | SRAM a[5] |
| io_in[20] | SRAM a[6] |
| io_in[21] | SRAM a[7] |
| io_in[22] | SRAM a[8] |
| io_in[23] | SRAM clk |
| io_out[24] | SRAM q[0] |
| io_in[25] | SRAM d[0] |
| io_in[26] | SRAM d[1] |
When io_in[n] is present in the table corresponding io_out[n] is connected to logic zero and corresponding io_oeb[n] to logic one. When io_out[n] is present corresponding io_oeb[n] is connected to logic zero.
One can also see that the SRAM block vss/vdd are connected to other pins than for the logic vss/vdd. The logic consists of buffers and logic one and zero cells. As the SRAM is not put in a deep nwell the SRAM vss and the logic vss will be connected to each other through the (higher resistive) bulk of the die. Separate vdd pins though will allow to measure the SRAM power consumption independently.
Layout of the unconnected SRAM block:
Layout of the caravan top:
The top level is fully generated from python code in the doitcode subdirectory. pydoit is used to generate the design with the provided dodo.py file in the top directory. The code depends on some external modules that are assumed to be installed:
As these code bases have still unstable APIs a mpw5 branch has been made in each of the repos with the state as for the tape-out.
The resulting GDS files is released under the LGPL 2.1 or later license. Some of the source code to generate the GDS is under the GPL 2.0 or later license.