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electronic devices
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Op-amp Applications
differential amplifier high-gain amplifier
voltage
level
shifter
output
stage
current mirror
current mirror current mirror
Differential Amplifier
The resultant output voltage is given by
Example
1) Design a differential voltage amplifier with va = 3 V, vb = 5 V, Ra = R1 = 12 kΩ
and RF = RX = 24 kΩ
2) Design a differential voltage amplifier with va = 3 V, vb = 5 V and let all
resistance have the same values of 20 kΩ
Voltage Follower
1. The output voltage equals the input voltage: vO = vS. This circuit is commonly
referred to as a voltage follower because its output voltage follows the input
voltage.
2. It has the inherent characteristics of a high input impedance (or resistance, typically
1010Ω) and a low output impedance (or resistance, typically 50 mΩ)
Integrator
The output voltage in the time domain becomes
Practical Inverting Integrator
In practice, as a result of its imperfections (such as
drift or input offset current) an op-amp produces an
output voltage even when the input signal is zero
and the capacitor will be charged by the small by
finite current through it. The capacitor prevents any
DC signal feeding back from the output terminal to
the input. As a result, the capacitor will charged
continuously and the output voltage will build up
until op-amp saturates.
Inverting Integrator
1. A resistor with a large value of RF is normally connected in parallel with the
capacitor of capacitance CF,.
2. RF provides the DC feedback and overcomes this saturation problem.
3. Time constant τF ( = RFCF) must be larger than the period Ts (= 1⁄fs) of the input
signal.
4. A ratio of 10 to 1 is generally adequate; that is, τF = 10Ts.
The output voltage in the time domain
becomes
Example
1. Design an integrator with frequency of the input is
fs = 500 Hz. The voltage gain should be unity at
a frequency of f1 = 1590 Hz. That is, the unity-
gain bandwidth is fbw = 1590 Hz. Let CF = 0.1 µF
2. The integrator in part (1) has Vcc = Vee = -12 V
and the maximum voltage swing = ±10 V. The
initial capacitor voltage is Vco = 0. Draw the
waveform of the output voltage for the input
voltage shown at the white boards.
Noninverting Integrator
The output voltage is given by
Differentiator
1. The value of Rx should be made equal to RF.
2. A differentiator circuit is useful in producing sharp trigger pulses to drive other
circuits.
3. A differentiator circuit behaves like a high-pass network.
4. The output voltage in the time domain is
Practical Inverting Differentiator
1. A modified circuit that is often utilized as a differentiator, in which a small
resistance R1 (< RF) is connected in series with C1 to limit the gain at high
frequencies.
2. This arrangement limits the high-frequency range.
Example Differentiator
The differentiator has R1 = 2 kΩ, RF = 10 kΩ and
C1 = 0.01 µF. Determine (a) the differentiator time
constant, (b) the gain limiting frequency and (c) the
maximum closed loop voltage gain Af(max)