NE5517, NE5517A, AU5517

http://onsemi.com

10

Voltage-Controlled Resistor (VCR)

Because an OTA is capable of producing an output current

proportional to the input voltage, a voltage variable resistor

can be made. Figure 26 shows how this is done. A voltage

+

R

) R

A

g

mMHOs at room

temperature. Figure 27 shows a Voltage Controlled Resistor

using linearizing diodes. This improves the noise

performance of the resistor.

Voltage-Controlled Filters

Figure 28 shows a Voltage Controlled Low-Pass Filter.

octave with the −3 dB point being defined by the given

equations. Operating in the same manner, a Voltage

Controlled High-Pass Filter is shown in Figure 29. Higher

order filters can be made using additional amplifiers as

shown in Figures 30 and 31.

Voltage-Controlled Oscillators

Figure 32 shows a voltage-controlled triangle-square

wave generator. With the indicated values a range from

to 10

mA.

Please notice the differential input voltage is not allowed

to be above 5.0 V.

With a slight modification of this circuit you can get the

sawtooth pulse generator, as shown in Figure 33.

APPLICATION HINTS

mirror ratio should be as accurate as possible over the entire

current range. A current mirror with only two transistors is

not recommended. A suitable current mirror can be built

with a PNP transistor array which causes excellent matching

and thermal coupling among the transistors. The output

current range of the DAC normally reaches from 0 to

−2.0 mA. In this application, however, the current range is

W) to 0 to −1.0 mA.

I

V

REF

R

REF

+ 2 @ 5V

10k

W +

1mA

−VCC

4

3

−

+

NE5517/A

8

VOUT

−VCC

11

+VCC

RX

5

IO

2

R

7

INT

INT

C

+VCC

VC

R

X +

R

) R

A

g

M @

R

A

Figure 26. VCR

30k

W

200

W

200

W

100k

W

10k

W

−VCC

4

3

NE5517/A

8

−VCC

11

+VCC

RX

5

ID

2

R

7

INT

INT

C

+VCC

VC

+VCC

VOS

RP

1

6

Figure 27. VCR with Linearizing Diodes

30k

W

1k

W

100k

W

10k

W