LM13700MX National Semiconductor, LM13700MX Datasheet - Page 12

• Manufacturer Part Number: LM13700MX
• Description: IC,Operational Amplifier,DUAL,BIPOLAR,SOP,16PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM13700MX

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Voltage Controlled Resistors
Voltage Controlled Filters
OTA’s are extremely useful for implementing voltage con-
trolled filters, with the LM13700 having the advantage that
the required buffers are included on the I.C. The VC Lo-Pass
Filter of Figure 11 performs as a unity-gain buffer amplifier at
frequencies below cut-off, with the cut-off frequency being
the point at which X
(R/R
single RC roll-off (6 dB per octave) of the input signal ampli-
tude with a −3 dB point defined by the given equation, where
A
). At frequencies above cut-off the circuit provides a
C
/g
m
equals the closed-loop gain of
FIGURE 9. Voltage Controlled Resistor with Linearizing Diodes
FIGURE 8. Voltage Controlled Resistor, Single-Ended
(Continued)
12
g
shows a VC High-Pass Filter which operates in much the
same manner, providing a single RC roll-off below the de-
fined cut-off frequency.
Additional amplifiers may be used to implement higher order
filters as demonstrated by the two-pole Butterworth Lo-Pass
Filter of Figure 13 and the state variable filter of Figure 14.
Due to the excellent g
filters perform well over several decades of frequency.
m
is again 19.2 x I
ABC
m
tracking of the two amplifiers, these
at room temperature. Figure 12
00798115
00798116