In this section:
Ring oscillator structures and measurement ............................ 2-1
Software description ................................................................. 2-1
Making a measurement ............................................................ 2-2
Ring oscillator structures and measurement
The main purpose of ring oscillator structures is to allow chip designers to characterize the switching
speed and propagation delays of logic gates. Propagation delay is calculated using the following
formula:
Figure 1: Propagation delay formula
where:
n
is the number of stages in the CMOS inverter chain
f
is the measured frequency of the circuit
Using a spectrum analyzer (instead of a frequency counter) is necessary because the signal
frequency of the ring oscillator is often in excess of several hundred mega hertz. This signal
frequency is well beyond the measurement capability of frequency counters when connected through
a tester.
Software description
There are two types of routines provided in the KIScope library:
•
Measurement routines to measure the signal characteristics of the inverter chain CMOS ring
oscillators.
•
Control routines to build custom measurement routines. Using the control routines provides
lower-level (and more direct) control of the scope card.
The measurement routines included with this software were built from the control routines.
Section 2
Basic Operations
