100µA

100µA

±

±

40k

40k

0.01µF

0.01µF

1N4148

1N4148

1N4148

1N4148

(e) Bidirectional 200µA

cascoded current source.

100µA

100µA

40k

40k

0.01µF

0.01µF

(d) Floating 200µA cascoded

current source.

100µA

L

o

a

d

+V

S

(a) Compliance approximate

to Gnd. HV compliance

limited by FET breakdown.

100µA

L

o

a

d

+V

S

(b) Compliance to +V – 5V.

High

Low

100µA

33k

0.01µF

S

100µA

L

o

a

d

+V

S

(c)

27k

5.1V

1N4689

NOTES: (1) FET cascoded current sources offer improved output impedance and high frequency operation. Circuit in (b)

also provides improved PSRR. (2) For current sinks (Circuits (a) and (b) only), invert circuits and use “N” channel JFETS.

REF200

SBVS020B – SEPTEMBER 2000 – REVISED JULY 2015

www.ti.com

System Examples (continued)

Figure 23. FET Cascode Circuits

14

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