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–

Q3

Q2

Q4

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–

Q2

Q1

Q4

Q3

V–

Q2

Q1

Q4

Q3

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

10V

R