4

Test Circuit

An external capacitor C is charged and discharged by two

current sources. Current source #2 is switched on and off by a

flip-flop, while current source #1 is on continuously. Assuming

that the flip-flop is in a state such that current source #2 is off,

and the capacitor is charged with a current I, the voltage

across the capacitor rises linearly with time. When this voltage

reaches the level of comparator #1 (set at 2/3 of the supply

voltage), the flip-flop is triggered, changes states, and

releases current source #2. This current source normally

carries a current 2I, thus the capacitor is discharged with a

net-current I and the voltage across it drops linearly with time.

When it has reached the level of comparator #2 (set at 1/3 of

the supply voltage), the flip-flop is triggered into its original

state and the cycle starts again.

Four waveforms are readily obtainable from this basic

generator circuit. With the current sources set at I and 2I

respectively, the charge and discharge times are equal. Thus

a triangle waveform is created across the capacitor and the

flip-flop produces a square wave. Both waveforms are fed to

buffer stages and are available at pins 3 and 9.

Detailed Schematic

ICL8038

456

9

2

12

11

10

8

7

N.C.

C

3300pF

82K

10K

10K

10K

-10V

3

+10V

FIGURE 1. TEST CIRCUIT

38

11K

39K

7

8

5

4

COMPARATOR

4K

5K

5K

5K

27K

27K

BUFFER AMPLIFIER

27K

4.7K

4.7K

27K

620

1.8K

100

100

100

30K

40K

10K

15K

1K

3

10

270

2.7K

470

800

2

10K

2.7K

800

FLIP-FLOP

SINE CONVERTER

6

V+

1

12

5.2K

200

375

330

1600

330

375

200

5.6K

82K

2.7K

10K

33K

33K

33K

33K

33K

33K

33K

33K

CURRENT SOURCES

9

11

ICL8038