551 PVTMonitorSuite :: Quicker, easier and cheaper to make your own chip!

How it works

PVTMonitorSuite integrates ring oscillators and flip-flop-based measurement circuits to quantify the timing characteristics of digital logic.

The suite supports the following measurements:

An inverter-based ring oscillator provides high-resolution estimates of gate propagation delay of an inverter ($t_{pd, INV}$).
A NAND2-based ring oscillator provides high-resolution estimates of gate propagation delay of NAND2 ($t_{pd, NAND2}$).
Standard, DICE, and LEAP-DICE D flip-flops measure clock-to-Q and setup timing ($t_{clkq} + t_{setup}$).
Clock skew timing ($t_{skew}$) is determined using a time digitizer between two clock signals.

High-speed counters driven by the ring oscillators convert these delays into digital values, enabling precise evaluation of process, voltage, and temperature variations on a fully digital, open-access platform.

To meet TinyTapeout’s requirements, no standard cells from the GF180MCU PDK process are used, and the design passes all strict error and warning checks.

How to test

Measure $t_{pd, INV}$

Connect uo_out[0] to your equipment to measure frequency.
Turn on ui_in[0].
Measure the frequency.
Calculate $t_{pd, INV} = \frac{1}{32 \times 51 \times f}$.

Measure $t_{pd, NAND2}$

Connect uo_out[1] to your equipment to measure frequency.
Turn on ui_in[0].
Measure the frequency.
Calculate $t_{pd, NAND2} = \frac{1}{32 \times 41 \times f}$.

Measure $t_{clkq} + t_{setup}$ of standard D-FF

Connect ui_in[1] to a device that generates exactly 50 MHz.
Set ui_in[7:5] to 3'b000, to choose measurement of $t_{clkq} + t_{setup}$.
Turn off ui_in[3].
Turn off ui_in[2] to reset.
Turn on ui_in[2].
Turn on ui_in[3] to start.
Read uio.
Calculate $t_{clkq} + t_{setup} = \frac{uio \times 20}{16} - 2 \times t_{pd, NAND2}$.

Measure $t_{clkq} + t_{setup}$ of DICE D-FF

Connect ui_in[1] to a device that generates exactly 50 MHz.
Set ui_in[7:5] to 3'b001, to choose measurement of $t_{clkq} + t_{setup}$.
Turn off ui_in[3].
Turn off ui_in[2] to reset.
Turn on ui_in[2].
Turn on ui_in[3] to start.
Read uio.
Calculate $t_{clkq} + t_{setup} = \frac{uio \times 20}{16}$.

Measure $t_{clkq} + t_{setup}$ of Leap DICE D-FF

Connect ui_in[1] to a device that generates exactly 50 MHz.
Set ui_in[7:5] to 3'b011, to choose measurement of $t_{clkq} + t_{setup}$.
Turn off ui_in[3].
Turn off ui_in[2] to reset.
Turn on ui_in[2].
Turn on ui_in[3] to start.
Read uio.
Calculate $t_{clkq} + t_{setup} = \frac{uio \times 20}{16}$.

Measure $t_{skew}$

Connect ui_in[1] to a device that generates exactly 50 MHz.
Connect ui_in[4] to a device of the target clock.
Set ui_in[7:5] to 3'b100, to choose measurement of $t_{skew}$.
Turn off ui_in[2] to reset.
Turn on ui_in[2] to start.
Read uio.
Calculate $t_{skew} = uio \times t_{pd, INV}$.

External hardware

An equipment to measure frequency.
A device that generates a precise 50 MHz signal, such as a ceramic resonator.
A device that generates the target clock.

#	Input	Output	Bidirectional
0	enable_ring_osc	inv_ring_osc_signal	counter_output[0]
1	measurement_clock	nand2_ring_osc_signal	counter_output[1]
2	reset_counter_n		counter_output[2]
3	d_input		counter_output[3]
4	target_clock		counter_output[4]
5	select[0]		counter_output[5]
6	select[1]		counter_output[6]
7	select[2]		counter_output[7]

551 PVTMonitorSuite