Fundamental Devices:
• operational amplifier
• comparator, Schmitt trigger
• linear gates
Operational amplifier (op-amp)
V+, V- positive and negative inputs
Vout output
VS+ , VS- positive and negative power supply (12-18 Volts)
Note: VS+ same as VDD, VCC, VCC+
VS- same as VSS, VEE, VCC-
Op-amp is a high-gain voltage differential amplifier;
typical gain G is in the range 100,000-200,000;
it amplifies the difference in the voltage applied to the pair of inputs
In typical usage op-amp is controlled by negative feedback, as shown:
• can be used as either an ‘inverting’ (negative feedback)
or a ‘non-inverting’ (positive feedback) voltage amplifier
• no negative feedback, the amplifier is said to be running "open loop"
Because the open-loop gain is typically very large, op-amps are not usually used
without negative feedback. Unless the differential input voltage is extremely small,
open-loop operation results in op-amp saturation
=Rf
=Ri
Inverting op-amp
(negative feedback)
Vout = −
Rf
Ri
Vin
Open loop=no feedback
Vout = Vin ⋅ Gopen loop
Gopen loop =
Vout
Vin
The ideal op-amp has infinite open-loop gain – this is a model.
Real amps only approach this model.
Limitations:
Finite gain;
Finite input resistance
Non-zero output resistance
Temperature effects
To a first approximation, the gain of a typical op-amp is inversely
proportional to frequency.
Gain & Frequency
Gain is fairly uniform at low frequencies,
but tends to fall away at high frequencies
Historical facts: 1952- K2-W first op-amp, G.A. Philbrick lab
1963- uA702 first solid-state op-amp by Bob Widlar, Fairchild Semiconductors,
supply voltages +12 and -6 volts, burn out when temporarily shorted
1965- uA709 by Bob Widlar, high gain, a larger bandwidth, lower input current,
supply voltage of approximately +/- 15 Volt DC
1967- LM101 more versatile op-amp version- gain up to 160K and operation range,
'short-circuit' protection, and simplified frequency compensation.
In 1968 improved version of LM101 was LM101A, National Semiconductor
1974- RC4558 first multiple op amp device, which uses NPN input transistors,
Raytheon Semiconductor's
In dated sequence, the op-amp developed like this: 1963-uA702, 1965-uA709,
1967-LM101/LH101, 1968-uA741, 1974-RC4558/LM324, 1975-CA3130/LF355,
and in 1976 the TL084...
Since 1976 the types of op amps have increased almost daily
K2-W op-amps from
George A.Philbrick’s lab (1952).
Detailed diagram of the common 741 op-amp
Absolute Maximum Parameters (741):
Typical applications of solid-state
integrated circuit operational amplifiers:
1 Linear circuit applications
1.1 Differential amplifier
1.1.1 Amplified difference
1.1.2 Difference amplifier
1.2 Inverting amplifier
1.3 Non-inverting amplifier
1.4 Voltage follower
1.5 Summing amplifier
1.6 Integrator
1.7 Differentiator
1.8 Comparator
1.9 Instrumentation amplifier
1.10 Schmitt trigger
1.11 Inductance gyrator
1.12 Zero level detector
1.13 Negative impedance converter (NIC)
2 Non-linear configurations
2.1 Precision rectifier
2.2 Peak detector
2.3 Logarithmic output
2.4 Exponential output
3 Other applications
audio and video pre-amplifiers and buffers
differentiators and integrators
filters
voltage regulator and current regulator
analog-to-digital converter
digital-to-analog converter
The negative feedback connection is the most typical use of an op-amp,
but many different configurations are possible, making it one of the most
versatile of all electronic building blocks.
Non-inverting op-amp
Comparator
Integrating op-amp
Schmitt trigger
Comparator
Differentiating op-amp
Peak detector
-is a circuit that compares two analog signals
and produces a one bit digital signal
-op-amp without feedback
V+
V-
+
-
Input voltage not exceed the power voltage
The comparator output satisfies the following rules:
-when V+ is larger than V- the output bit is 1.
-when V+ is smaller than V- the output bit is 0
http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML
Comparator- no feedback:
Vout = Vs sgn(V+ − V− )
⎛ −1 , x < 0 ⎞
where sgn x = ⎜ 0 , x = 0 ⎟
⎜
⎟
⎜ 1 , x > 0⎟
⎝
⎠
signum function
and Vs is the power supply voltage
LM-339 a typical comparator chip.
internal circuitry LM339
Some applications of comparator:
constant fraction discriminator, flash ADC
The Schmitt trigger - a comparator with positive feedback
Schmitt trigger has some memory- hysteresis.
Symbol:
The threshold
T=
R1
Vsat
R2
can be adjusted by controlling
the resistances R1 and R2.
Threshold T changes
from − Τ = −
R1
R
Vsat to Τ = 1 Vsat
R2
R2
Vout
1
0
−Τ
∆
Τ
The choice of ∆ is important:
if ∆ is greater than the amplitude of the noise fluctuations
stuttering is eliminated.
the effect of using the Schmitt trigger:
A
B
C
A – input signal
B – comparator response
C – trigger response
Vin
Gates -electronic switch controlled by logical signal.
Two basic arrangements:
series
signal E
switch
gate
1
closed
open
0
open
closed
shunt
signal E
switch
gate
1
closed
closed
0
open
open
series
Open switch exhibit capacitance and
closed switch exhibit small resistance.
As a result, the high frequency
will feed through closed gate.
shunt
Artifact : control signal may influence the output and
hence introduce the distortion (submicrosecond scale).
Consider shunt arrangement:
•Circuits are designed with balanced gates
to minimize the pedestal.
•While reducing pedestal short time shifts
between balanced gates result in spikes
in the output.
Some applications
1. Multiplexer
In this example,
3-phase time state generator and
three linear gates; gates are of series type
2. Event selection
Here, gate signal is generated when
event “B” occurs.
3. Op-amp with gate selected feedback impedances
gates are series type;
impedance network works as a filter
+