Introduction to the opamp chooser
The characteristics of the ideal opamp are easy to define, and include the following:
Zero power consumption.
Zero offset voltage.
Zero bias current
Infinite slew rate
Zero output impedance
Real devices deviate from this ideal, and engineering often consists of
a search for the opamp which has the smallest compromise for a specific
application. For more information on opamps go to the opamps page.
The chooser program allows the user to shortlist some suitable devices
by excluding inappropriate devices. It is not intended to provide a
final recommendation, but rather to speed up the preliminary
search for devices which can then be analysed in greater detail.
Device characteristics can take a variety of forms, and are
organised into columns.
Scalar characteristics are represented by simple
floating point numbers. Quiescent current consumption and
bandwidth are examples of scalar characteristics. Devices can be excluded
from the shortlist if the characteristic is greater or less than limits
entered by the user. Entering 1 in the offset voltage maximum value
field will reject all those devices with an offset voltage of more than
1mV. Devices will also be sorted by that characteristic, so the device
with the lowest offset voltage appears at the top of the list. Sorting
always puts the best device at the top, where best means the most
If the user wants devices that fall into a range, both a minimum and a
maximum value can be entered. If the maximum value is less than the
minimum, then all devices will be excluded.
If the value for a scalar device characteristic is invalid (e.g.
bandwidth at gain 1 for a device which is not stable at gain 1) or
unknown, then the entry is blank. The device will be excluded if a
limit is set on this characteristic.
Some device characteristics are a simple exclusive
choice. The device package and pinout are typical examples. All
the choices are contained in a list, and each choice can be separately
included or excluded. If the user is looking for a device in a dual in
line through hole package, the PDIP and CERDIP options would be
included (by being checked), and the SO, TSSOP SOT23 etc. options would
be excluded (by clearing the checkboxes).
A table entry may be a URL, and clicking on the URL
will open a web browser. No selections are possible on URLs, or on
plain text fields.