FN957.10 July 11, 2005 Wien Bridge Oscillator Another application of the CA3140 that makes excellent use of its high input impedance, high slew" />
參數(shù)資料
型號(hào)： CA3140AEZ
廠商： Intersil
文件頁(yè)數(shù)： 8/23頁(yè)
文件大小： 0K
描述： IC OPAMP BIMOS 4.5MHZ 8DIP
標(biāo)準(zhǔn)包裝： 50
放大器類型： 通用
電路數(shù)： 1
轉(zhuǎn)換速率： 9 V/µs
增益帶寬積： 4.5MHz
電流 - 輸入偏壓： 10pA
電壓 - 輸入偏移： 2000µV
電流 - 電源： 4mA
電流 - 輸出 / 通道： 40mA
電壓 - 電源，單路/雙路(±)： 4 V ~ 36 V，±2 V ~ 18 V
工作溫度： -55°C ~ 125°C
安裝類型： 通孔
封裝/外殼： 8-DIP（0.300"，7.62mm）
供應(yīng)商設(shè)備封裝： 8-PDIP
包裝： 管件
產(chǎn)品目錄頁(yè)面： 1233 (CN2011-ZH PDF)
16
FN957.10
July 11, 2005
Wien Bridge Oscillator
Another application of the CA3140 that makes excellent use
of its high input impedance, high slew rate, and high voltage
qualities is the Wien Bridge sine wave oscillator. A basic Wien
Bridge oscillator is shown in Figure 21. When R1 = R2 = R
and C1 = C2 = C, the frequency equation reduces to the
familiar f = 1/(2
πRC) and the gain required for oscillation,
AOSC is equal to 3. Note that if C2 is increased by a factor of
four and R2 is reduced by a factor of four, the gain required
for oscillation becomes 1.5, thus permitting a potentially
higher operating frequency closer to the gain bandwidth
product of the CA3140.
Oscillator stabilization takes on many forms. It must be
precisely set, otherwise the amplitude will either diminish or
reach some form of limiting with high levels of distortion. The
element, RS, is commonly replaced with some variable
resistance element. Thus, through some control means, the
value of RS is adjusted to maintain constant oscillator output.
A FET channel resistance, a thermistor, a lamp bulb, or other
device whose resistance increases as the output amplitude
is increased are a few of the elements often utilized.
Figure 22 shows another means of stabilizing the oscillator
with a zener diode shunting the feedback resistor (RF of
Figure 21). As the output signal amplitude increases, the
zener diode impedance decreases resulting in more
feedback with consequent reduction in gain; thus stabilizing
the amplitude of the output signal. Furthermore, this
combination of a monolithic zener diode and bridge rectifier
circuit tends to provide a zero temperature coefficient for this
regulating system. Because this bridge rectifier system has
no time constant, i.e., thermal time constant for the lamp
bulb, and RC time constant for filters often used in detector
networks, there is no lower frequency limit. For example, with
1
F polycarbonate capacitors and 22M for the frequency
determining network, the operating frequency is 0.007Hz.
As the frequency is increased, the output amplitude must be
reduced to prevent the output signal from becoming slew-
rate limited. An output frequency of 180kHz will reach a slew
rate of approximately 9V/
s when its amplitude is 16V
P-P.
Simple Sample-and-Hold System
Figure 23 shows a very simple sample-and-hold system
using the CA3140 as the readout amplifier for the storage
capacitor. The CA3080A serves as both input buffer amplifier
and low feed-through transmission switch (see Note 13).
System offset nulling is accomplished with the CA3140 via
its offset nulling terminals. A typical simulated load of 2k
and 30pF is shown in the schematic.
In this circuit, the storage compensation capacitance (C1) is
only 200pF. Larger value capacitors provide longer “hold”
periods but with slower slew rates. The slew rate is:
NOTE:
13. AN6668 “Applications of the CA3080 and CA 3080A High
Performance Operational Transconductance Amplifiers”.
NOTES:
f
1
2
π R
1C1R2C2
-------------------------------------------
=
A
OSC
1
C
1
C
2
-------
R
2
R
1
-------
++
=
A
CL
1
R
F
R
S
--------
+
=
C1
R2
R1
C2
OUTPUT
RF
RS
+
-
FIGURE 21. BASIC WIEN BRIDGE OSCILLATOR CIRCUIT
USING AN OPERATIONAL AMPLIFIER
8
5
4
3
1
9
6
CA3109
DIODE
ARRAY
+15V
0.1
F
0.1
F
-15V
2
6
7
4
+
CA3140
-
SUBSTRATE
OF CA3019
0.1
F
7
7.5k
3.6k
500
OUTPUT
19VP-P TO 22VP-P
THD <0.3%
3
R2
C2
1000pF
1000
pF
C1
R1
R1 = R2 = R
50Hz, R = 3.3M
100Hz, R = 1.6M
1kHz, R = 160M
10kHz, R = 16M
30kHz, R = 5.1M
2
FIGURE 22. WIEN BRIDGE OSCILLATOR CIRCUIT USING
CA3140
+15V
3.5k
30pF
2
6
1
+
CA3140
-
SIMULATED LOAD
NOT REQUIRED
100k
INPUT
0.1
F
7
0.1
F
-15V
2k
3
400
200pF
6
4
5
7
4
+
CA3080A
-
0.1
F
+15V
-15V
200pF
2k
2
3
5
2k
STROBE
SAMPLE
HOLD
-15
0
30k
1N914
2k
C1
FIGURE 23. SAMPLE AND HOLD CIRCUIT
dv
dt
------
I
C
----
0.5mA 200pF
2.5V
s
==
=
CA3140, CA3140A
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