Enhancement-load invertor
Table of Contents -
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9
R
S
In this section:
The enhancement load invertor
- The load line
- The transfer curve
- Noise margins
- Eye diagram
- Circuit layout
The enhancement load invertor
A circuit diagram of an enhancement load invertor is shown in the figure
below. It consist of two enhancement mode (normally off) transistors, one
used as the driver whose gate forms the input of the invertor and
a second transistor whose gate is connected to the drain and acts as a load
device:
enhload1.gif
The enhancement load invertor is the basic logic element of
the first transistor-only technology. The historic importance
of this technology is that only one type of transistor was used
which led to a simple process while being very space efficient since
no resistors are needed. This technology was quickly replaced with
depletion load circuits followed by complementary MOS circuits.
The simple process technology and the fact that all MOS circuit issues
are very similar to that of a full CMOS circuit technology makes the
enhancement mode circuit technology a useful topic of study.
The load line of the enhancement load is shown in the figure below. Shown are the
I-V characteristics of the driver transistor in addition to the load line of the
enhancement load device. Since the currrent through each
device must be the same as they are connected in series, the output voltage
can be otained at the intersection of the I-V curve at a specific gate voltage of the
driver and the load line. The result is shown in the
inset and the detailed procedure is described in the next section.
enhload6.gif
The detailed construction of the transfer curve which is obtained
by plotting the output of the invertor as a function of the
input is illustrated with the figure below:
enhload7.gif
The eye diagram contains the transfer curve as well as the transfer curve which
is plotted with the input voltage on the vertical axis and the output voltage
on the horizontal axis yielding the mirror image of the transfer curve mirrored by the
y = x plane.
enhload3.gif
© Bart J. Van Zeghbroeck, 1998