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CALEX
FaxFACTS:
321
1997
Models 152 & 155 Operational Amplifiers
http://www.calex.com
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
Description
The Model 152 is an economical, general purpose operational
amplifier featuring very low input bias current and high input
impedance. It is designed for applications involving high
source resistances. The Model 155 has all these same
features but is better suited for applications requiring low
voltage drift.
A versatile circuit building kit, the Model MK150, is available.
It makes it easy to connect an amplifier in a wide variety of
standard op-amp circuits. These include inverting and non-
inverting amplifier, integrator, summer, etc. A potentiometer
for nulling the input offset and test jacks are provided.
Inverting/Filter Amplifier
The basic inverting amplifier shown in Figure 1 is useful where
a signal inversion or a simple low/high pass filter function is
required. The basic inverting amplifiers are used where high
slew rate and or high linearity is needed.
Basic Design Equations:
GAIN ........................... G = R6 / (R1 + R14)
0.1 < G < 100
R6 + RLoad > 2 kohms
Either R1 or R14 can be zero ohms
(jumper) for convenience
INPUT IMPEDANCE... Zin = R1 +R14
BANDWIDTH .............. bw = 3 MHz/(1+G) in Hz
Value For R5............... R5 = Zin || R6
For a low pass filter function add C2 by the following equation,
Fc = 1 / (2 x pi x R6 x C2) 100 pF < C2 < 1 µF
Where Fc is the -3 dB frequency in Hz of the low pass function.
The roll off is 6 dB per octave or -20 dB per decade of
frequency.
FIGURE 1. Inverting Amplifier FIGURE 2. Inverting Summing Amplifier
Inverting Summing Amplifier
Figure 2 shows the basic inverting summing amplifier
configuration. This amplifier provides the function of summing
inputs and providing gain. The summed output can be low
pass filtered to reduce high frequency noise if required.
Basic Design Equations:
GAIN ........................... G1 = R6/(R1 +R14) Input to Pin H
G2 = R6/R2 Input to Pin K
G3 = R6/R3 Input to Pin L
G4= R6/R4 Input to Pin M
0.1 < G < 100 for any input
R6 || RLoad > 2k ohms
Either R1 or R14 can be zero ohms
(jumper) for convenience.
INPUT IMPEDANCE... Zin = (R1 +R14) or R2 or R3 or R4
BANDWIDTH .............. bw = 3 MHz/(1+R6/Zin) in Hz
Value For R5............... R5 = Zin ll R6
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CALEX
FaxFACTS:
321
1997
Models 152 & 155 Operational Amplifiers
http://www.calex.com
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
FIGURE 3. AC Coupled Amplifier
AC Coupled Inverting Amplifier
An AC coupled amplifier or high pass filter amplifier (Figure 3)
is also easy to construct with MK 150. This amplifier is useful
for audio and other applications where the DC content of the
signal is not important.
Basic Design Equations:
GAIN ........................... G = R6 / R14
0.1 < G < 100
R6 || RLoad > 2 kohms
INPUT IMPEDANCE... Zin = R14,
Midband: DC Zin = Infinity
BANDWIDTH .............. bw = 3 MHz/(1+G) in Hz
Value For R5............... R5 = R6
Value For C1............... C1 = 1/(2 x pi x Fc x R14) in Hz, where
Fc is the lower -3 dB cutoff of the
amplifier.
The low frequency roll off is +6 dB or +20 dB per decade of
increasing frequency. Pick C2 to minimize overshoot or
ringing with a small square wave input. Increasing C2 will
reduce overshoot and ringing at the output.
Non-inverting Amplifier
Figure 4. Shows the basic non-inverting amplifier circuit. The
non-inverting amplifier or voltage follower is useful where high
input impedance is required and or an in phase output voltage
is required.
Basic Design Equations:
GAIN ........................... G = 1 + R6 / (R14 + R1)
0.1 < G < 100
Either R14 or R1 can be zero ohms
for convenience
R6 || RLoad > 2 kohms
if R1 + R14 are not used the gain
is a precision +1 (voltage follower
mode).
INPUT IMPEDANCE... Zin = > 10 Meg
BANDWIDTH .............. bw = 3 MHz/G in Hz
Value For R5............... R5 = R6 || (R1 + R14)
The gain can be rolled off to a minimum gain of +1 by using
C2 in the circuit.
The Differentiator
The differentiator (also Figure 3) is basically a high pass filter
that has the useful property of producing an output voltage
that is proportional to the instantaneous derivative of the input
waveform.
Basic Design Equations:
Voltage Output............ Vo = -R6 x C1 x dVi/dt
Vo should be as low as possible for
maximum dynamic range.
Utility Gain Frequency Fc = 1/(2 x pi x R6 x C1)
Value for R5................R5 = R6
Value for R14 and C2 Select for minimum overshoot and
ringing on the output with a step
input. Increase R14 and or C2 to
reduce overshoot.
FIGURE 4. Non-inverting Amplifier Circuit
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CALEX
FaxFACTS:
321
1997
Models 152 & 155 Operational Amplifiers
http://www.calex.com
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
Specifications
FIGURE 6. MK150 Mounting Kit Dimensions
For Model 155-TP1, TP2, R12, R15 and Jumper for R11 are
factory installed.
For Model 152-TP1, TP2, R16, and Jumper for R11 are
factory installed.
FIGURE 5. MK150 Mounting Kit Schematic
FIGURE 7. Outline Dimensions
MODEL
152 MODEL
155
General Notes
When driving capacitive loads or shielded cables of greater
than 50pF remove the jumper for R11 and insert a 470 ohm
resistor. This will prevent oscillation that will appear as an
unstable DC offset to most measuring equipment.
The minimum value of load resistance is 2k ohms for a rated
output swing of ±10 Volts. The external load must be considered
along with the feedback resistance for the total load. For
reduced swings the output load can be increased up to a
maximum of 5 mA peak.
For optimum DC stability use single point “Star” grounds to
Pin B. This will prevent unwanted ground loops or “unexplained”
DC offsets.
When the MK150 is wired in a system and it appears that
something is wrong, remove the MK150 and test it individually
to make sure that it functions as expected. Then troubleshoot
the system from the transducer to the end, a function block
at a time.
If a high precision amplifier is required with a gain of 100 or
more, the 176/178 Instrumentation amplifiers are a much
better choice for most systems.
If all else fails please feel free to call our applications
engineers; we spend time trouble shooting our own systems
and can sometimes spot trouble right away. We even learn
new tricks from our customers!
To order the MK150 for use with the 152, specify the MK150
as MK150-152. For use with the 155, specify the MK150 as
MK150-155.
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