A resitive loaded and biased differential amplifier circuit is shown in figure. Neglecting the base currents and assuming matched transistors with VA = ∞,β = 100, w hat are the values of R_{c} and R_{E} to meet the following specifications?
Differential mode gain (double ended) = 500,
Common mode rejection ratio = 500,
Differential mode input resistance = 2 MQ.
In the level shifter circuit shown in figure beiow, the internal drop across each diode V_{D} = V_{BE2} = 0.7 V and h_{fe} is very large.
The value of R for V_{0} to become zero is
The aiven circuit is redrawn as shown below.
Writing loop equation containing two diodes and
A differential amplifier, amplifies
The goal of designing differential amplifiers is to minimize the effect of commonmode input signal and amplify the difference of the voltages between the two input lines.
Most of linear ICs are based on the two transistor differential amplifier because of its
A differential amplifier has RL = 10 kΩ(equal values in both collectors), hie = 1 kΩ, R_{e} = 50 kΩ, h_{te} = 100. The common mode gain is given by
Common mode gain,
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In a singlestage differential amplifier, the output offset voltage is basically dependent on the mismatch of
In single stage differential amplifier, the output offset voltage is basically dependent on the mismatch of I_{B} and β.
Assertion (A): It is not so easy to design d.c. amplifiers using transistors.
Reason (R): The values of h_{fe} ,V_{BE }and I_{CBO} vary with temperature.
The values of h_{FE}, V_{BE} and I_{CB0} vary with temperature and due to the variation in any of these quantities the output voltage may change which may not be distinguished from a change in the input signal voltage, Due to this reason it is not so easy to design d.c. amplifiers using transistors. Hence, both assertion and reason are true and reason is the correct explanation of assertion.
Assertion (A): The ability of a differential amplifier to reject a differential mode signal is called its “figure of merit”.
Reason (R): The ideal value of figure of merit of a differential amplifier is infinite.
Assertion is not true because “figure of merit” (or CM MR) of a differential amplifier is to reject a common mode signal (v_{C}).
A differential amplifier has (i) CMMR= 1000 and (ii) CMRR= 10000.
The first set of inputs is V_{1}= 100 μV and V_{2}, = 100μV.
The second set of inputs is V_{1}= 1100 μV and V_{2} = 900 μV.
What is the percentage difference in output voltage obtained for the two sets of input voltages?
we know that
Now,
From equation (iii) and (iv), the percentage difference in output voltage obtained for the two sets of input voltages
The Qpoint (V_{c} and I_{B}) for the differential amplifier shown in figure below is given by:
Also
Hence, both transistors of the differential amplifier are biased at a Qpoint having l_{B} = 1.09 μA and V_{c}=7.9V.
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