MAT14
Rev. A | Page 8 of 12
THEORY OF OPERATION
APPLICATIONS INFORMATION
To minimize coupling between devices, tie one of the substrate
pins (Pin 4 or Pin 11) to the most negative circuit potential.
Note that Pin 4 and Pin 11 are internally connected.
Applications Current Sources
MAT14 can be used to implement a variety of high impedance
current mirrors as shown in Figure 15, Figure 16, and Figure 17.
These current mirrors can be used as biasing elements and load
devices for amplifier stages.
Q1
V–
I
REF
I
OUT
= I
REF
Q3
Q2
Q4
09045-015
Figure 15. Unity-Gain Current Mirror, I
OUT
= I
REF
The unity-gain current mirror shown in Figure 15 has an
accuracy of better than 1% and an output impedance of more
than 100 MΩ at 100 μA.
Figure 16 and Figure 17 each show a modified current mirror;
Figure 16 is designed for a current gain of two (2), and Figure 17
is designed for a current gain of one-half (½). The accuracy of
these mirrors is reduced from that of the unity-gain source due
to base current errors but remains better than 2%.
V–
I
REF
I
OUT
= 2(I
REF
)
Q2
Q1
Q4
Q3
09045-016
Figure 16. Current Mirror, I
OUT
= 2(l
REF
)
V–
I
REF
I
OUT
= 1/2(I
REF
)
Q2
Q1
Q4
Q3
09045-017
Figure 17. Current Mirror, I
OUT
= ½(I
REF
)
Figure 18 is a temperature independent current sink that has an
accuracy of better than 1% at an output current of 100 μA to 1 mA.
A Schottky diode acts as a clamp to ensure correct circuit startup at
power-on. Use 1% metal film type resistors in this circuit.
+15V
2
4
2
3
7
HP
5082-2811
4
6
6
R
R
100pF
R
2
1
3
6
7
5
9
8
10
13
14
12
R
–15V
R R
MAT14
OP1177
ADR01
I
OUT
I
OUT
I
OUT
I
OUT
=
10V
R
09045-018
Figure 18. Temperature Independent Current Sink, I
OUT
= 10 V/R
