CA3280, CA3280A
of the CA3280. The linearization diode impedance also
decreases as the diode bias current increases, which further
loads the input. The diodes, in addition to acting as a
linearization network, also operate as an additional
attenuation system to accommodate input signals in the volt
range when they are applied through appropriate input
resistors.
Figure 10 shows a triangle wave to sine wave converter
using the CA3280. Two 100kΩ resistors are connected
between the differential amplifier emitters and V+ to reduce
the current flow through the differential amplifier. This allows
the amplifier to fully cut off during peak input signal
excursions. THD is appropriately 0.37% for this circuit.
V+
RD = SMALL SIGNAL DIODE
IMPEDANCE
RD ≈ID5(2mΩA)
x 1.34 =
70
ID
VOA
IABC
ID
V-
FIGURE 4. VOA SHOWING LINEARIZATION DIODES AND
CURRENT DRIVE
+15V
2kΩ
DIFFERENTIAL
INPUT 2kΩ
68kΩ
14
3
16 +
1/2
CA3280
13
15 -
4
1
-15V
SINGLE-
ENDED
OUTPUT
10kΩ
FIGURE 6. DIFFERENTIAL TO SINGLE ENDED CONVERTER
RD
VOA
ID IABC
FIGURE 5. BLOCK DIAGRAM OF LINEARIZED VOA
10VP-P
INPUT
600Ω
10kΩ
V+
100kΩ
330kΩ
V-
10kΩ
68kΩ
1
14
16 +
1/2
CA3280
15 -
4
3
V+ = +15V
OUTPUT
21VP-P
14mV AGC
FEEDTHRU
400µV
NOISE AT
MAX GAIN
13
15kΩ
20kΩ
V- = -15V
VOLTAGE
CONTROL
FIGURE 7. TYPICAL GAIN CONTROL CIRCUIT
6