Datasheet CA3140, CA3140A (Intersil) - 10

CA3140, CA3140A
placed across the input to the CA3080A to give a logarithmic
7 TA = 125oC
analog indication of the function generator’s frequency.
FOR METAL CAN PACKAGES 6 V) DIFFERENTIAL DC VOLTAGE
Analog frequency readout is readily accomplished by the
m ( (ACROSS TERMINALS 2 AND 3) = 2V T 5
means described above because the output current of the
IF OUTPUT STAGE TOGGLED H
CA3080A varies approximately one decade for each 60mV
S 4
change in the applied voltage, V
GE
ABC (voltage between
A T
Terminals 5 and 4 of the CA3080A of the function generator).
L 3 O
Therefore, six decades represent 360mV change in V
V
ABC.
T E 2 S
Now, only the reference voltage must be established to set
F DIFFERENTIAL DC VOLTAGE OF (ACROSS TERMINALS 2 AND 3) = 0V
the lower limit on the meter. The three remaining transistors
1 OUTPUT VOLTAGE = V+ / 2
from the CA3086 Array used in the sweep generator are
0
used for this reference voltage. In addition, this reference
0 500 1000 1500 2000 2500 3000 3500 4000 4500
generator arrangement tends to track ambient temperature
TIME (HOURS)
variations, and thus compensates for the effects of the
FIGURE 9. TYPICAL INCREMENTAL OFFSET VOLTAGE
normal negative temperature coefficient of the CA3080A
SHIFT vs OPERATING LIFE
VABC terminal voltage.
Super Sweep Function Generator
Another output voltage from the reference generator is used A function generator having a wide tuning range is shown in to insure temperature tracking of the lower end of the Figure 10. The 1,000,000/1 adjustment range is Frequency Adjustment Potentiometer. A large series accomplished by a single variable potentiometer or by an resistance simulates a current source, assuring similar auxiliary sweeping signal. The CA3140 functions as a non- temperature coefficients at both ends of the Frequency inverting readout amplifier of the triangular signal developed Adjustment Control. across the integrating capacitor network connected to the output of the CA3080A current source. To calibrate this circuit, set the Frequency Adjustment Potentiometer at its low end. Then adjust the Minimum Buffered triangular output signals are then applied to a Frequency Calibration Control for the lowest frequency. To second CA3080 functioning as a high speed hysteresis establish the upper frequency limit, set the Frequency switch. Output from the switch is returned directly back to the Adjustment Potentiometer to its upper end and then adjust input of the CA3080A current source, thereby, completing the Maximum Frequency Calibration Control for the the positive feedback loop maximum frequency. Because there is interaction among The triangular output level is determined by the four 1N914 these controls, repetition of the adjustment procedure may level limiting diodes of the second CA3080 and the resistor be necessary. Two adjustments are used for the meter. The divider network connected to Terminal No. 2 (input) of the meter sensitivity control sets the meter scale width of each CA3080. These diodes establish the input trip level to this decade, while the meter position control adjusts the pointer switching stage and, therefore, indirectly determine the on the scale with negligible effect on the sensitivity amplitude of the output triangle. adjustment. Thus, the meter sensitivity adjustment control calibrates the meter so that it deflects 1/6 of full scale for Compensation for propagation delays around the entire loop each decade change in frequency. is provided by one adjustment on the input of the CA3080. This adjustment, which provides for a constant generator
Sine Wave Shaper
amplitude output, is most easily made while the generator is The circuit shown in Figure 12 uses a CA3140 as a voltage sweeping. High frequency ramp linearity is adjusted by the follower in combination with diodes from the CA3019 Array single 7pF to 60pF capacitor in the output of the CA3080A. to convert the triangular signal from the function generator to a sine-wave output signal having typically less than 2% THD. It must be emphasized that only the CA3080A is The basic zero crossing slope is established by the 10kΩ characterized for maximum output linearity in the current potentiometer connected between Terminals 2 and 6 of the generator function. CA3140 and the 9.1kΩ resistor and 10kΩ potentiometer
Meter Driver and Buffer Amplifier
from Terminal 2 to ground. Two break points are established Figure 11 shows the CA3140 connected as a meter driver by diodes D1 through D4. Positive feedback via D5 and D6 and buffer amplifier. Low driving impedance is required of establishes the zero slope at the maximum and minimum the CA3080A current source to assure smooth operation of levels of the sine wave. This technique is necessary because the Frequency Adjustment Control. This low-driving the voltage follower configuration approaches unity gain impedance requirement is easily met by using a CA3140 rather than the zero gain required to shape the sine wave at connected as a voltage follower. Moreover, a meter may be the two extremes. 10 FN957.10 July 11, 2005