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NE5517DR2 View Datasheet(PDF) - ON Semiconductor

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NE5517DR2 Datasheet PDF : 14 Pages
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NE5517, NE5517A, AU5517
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
presented at the RX terminals forces a voltage at the input.
This voltage is multiplied by gM and thereby forces a current
through the RX terminals:
Rx
+
R
gM
)
)
RA
RA
where gM is approximately 19.21 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.
The circuit is a unity gain buffer until XC/gM is equal to
R/RA. Then, the frequency response rolls off at a 6dB per
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
2.0 Hz to 200 kHz is possible by varying IABC from 1.0 mA
to 10 mA.
The output amplitude is determined by IOUT × ROUT.
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
To hold the transconductance gM within the linear range,
IABC should be chosen not greater than 1.0 mA. The current
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
set through RREF (10 kW) to 0 to −1.0 mA.
IDACMAX
+
2
@
VREF
RREF
+
2
@
5V
10kW
+
1mA
+VCC
200W 200W
3+
11
2
NE5517/A
4
−VCC
30kW
IO
5
7
C
8
RX
R
100kW
R ) RA
RX + gM @ RA
VC
INT
+VCC
VOUT
10kW
−VCC
INT
Figure 26. VCR
+VCC
1
ID
VOS
+VCC
RP
1kW
3
11
2
NE5517/A
6
4
−VCC
30kW
5
7
C
8
RX
R
100kW
VC
INT
+VCC
10kW
−VCC
INT
Figure 27. VCR with Linearizing Diodes
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