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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4508
Keywords: 4-20mA transmitters, precision current mirrors, current-sense resistor ratios
APPLICATION NOTE 4508
Precision Current-Sink/Source Circuits Configure
as Mirrors or Amplifiers
Nov 11, 2010
Abstract: The precision current mirrors shown allow you to transform one type of 4–20mA transmitter to
another, or to create a repeater for the purpose of extending the length of the current loop. The circuits
include an input-sink/output-sink mirror and an input-source/output-source mirror.
A similar version of this article appeared in the September 21, 2008 issue of EE Times magazine.
The 4–20mA transmitters used in industrial current-control loops can be implemented as powered
current sources, remote non-powered current sinks, or with several other I/O combinations.
A useful building block for some of these applications is a precision current mirror, which allows you to
transform one type of transmitter to another, or to create a repeater for the purpose of extending the loop
length. Circuit examples include an input-sink/output-sink mirror (Figure 1a), and an input-source/output-
source mirror (Figure 1b). These circuits have similar configurations but differ slightly in performance.
You can also build input-sink/output-source mirrors and input-source/output-sink mirrors by chaining one
circuit type to the other.
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