Schmitt Trigger MCQ Quiz - Objective Question with Answer for Schmitt Trigger - Download Free PDF

Explanation:

In the given Schmitt trigger circuit, we are required to find the output logic low level when V_CE(sat) = 0.1 V.

A Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the non-inverting input of a comparator or differential amplifier. Schmitt triggers are used to convert a noisy analog input signal into a clean digital output signal.

The output of a Schmitt trigger circuit switches between high and low voltage levels, depending on the input voltage and the threshold voltages set by the circuit. The output logic low level is the voltage level of the output when the circuit is in the low state, which typically occurs when the input voltage is below the lower threshold voltage.

In a Schmitt trigger circuit, the output stage is usually an open-collector or open-drain configuration. When the output is low, the transistor in the output stage is saturated, and the output voltage is approximately equal to the saturation voltage of the transistor, V_CE(sat).

Given that V_CE(sat) = 0.1 V, the output logic low level can be determined as follows:

Step-by-Step Solution:

1. Identify the saturation voltage of the transistor (V_CE(sat)). In this case, V_CE(sat) is given as 0.1 V.
2. In the low state, the output voltage is approximately equal to V_CE(sat).
3. Therefore, the output logic low level is 0.1 V.

However, the given options are:

• Option 1: 3.65 V
• Option 2: 3.85 V
• Option 3: 1.35 V
• Option 4: 1.15 V

Since the output logic low level is typically very close to V_CE(sat) (0.1 V), let's consider the given options:

• Option 1: 3.65 V
• Option 2: 3.85 V
• Option 3: 1.35 V
• Option 4: 1.15 V

Among these options, the one that aligns closest to the expected output logic low level is Option 3: 1.35 V. This value may represent the logic low level due to other factors in the circuit that might influence the saturation voltage slightly, but still, it is the closest to the given V_CE(sat).

Correct Option Analysis:

The correct option is:

Option 3: 1.35 V

This option is closest to the expected output logic low level given the saturation voltage of the transistor in the Schmitt trigger circuit. The value of 1.35 V may be due to additional voltage drops or other circuit elements, but it is the best match among the provided options.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: 3.65 V

This option is much higher than the expected output logic low level. A typical logic low level in a Schmitt trigger circuit should be close to the saturation voltage of the transistor, which is much lower than 3.65 V.

Option 2: 3.85 V

Similar to Option 1, this value is also too high to be considered as the output logic low level. The saturation voltage of the transistor in the output stage would not typically result in such a high voltage for the logic low state.

Option 4: 1.15 V

While this option is closer to the expected output logic low level than Options 1 and 2, it is still higher than the given V_CE(sat) of 0.1 V. However, it is relatively close and could be a result of other circuit elements affecting the voltage slightly.

Conclusion:

Understanding the behavior of the Schmitt trigger circuit and the impact of the transistor's saturation voltage is essential for correctly identifying the output logic levels. The output logic low level is determined by the saturation voltage of the transistor, which is given as 0.1 V in this case. Among the provided options, Option 3: 1.35 V is the closest match, accounting for potential minor variations in the circuit. This analysis highlights the importance of considering all factors in the circuit when determining the output logic levels.

Schmitt Trigger:

• It is a comparator circuit with positive feedback.
• It is a Bi-stable circuit, having two stable states (+Vsat and -Vsat).
• In this, input sine-wave is converted to a square wave
• The output voltage changes its states whenever the input voltage exceeds certain voltage levels (i.e. VUT & VLT)

∴ The input sine-wave converted into a square wave

The correct option is 3

Concept:

• A Schmitt trigger is basically an inverting comparator circuit with positive feedback. 
• The function of the Schmitt trigger is to convert any regular or irregular-shaped input waveform into a square wave output voltage or pulse.
• Thus, it can shape a wave and also called as a squaring circuit and can be used as a square wave generator.
• Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the non-inverting input of a comparator or differential amplifier.
• It is an active circuit that converts an analog input signal to a digital output signal.
• The circuit is named a "trigger" because the output retains its value until the input changes sufficiently to trigger a change.
• In the non-inverting configuration, when the input is higher than a chosen threshold, then output is high.
• When the input is below a different (lower) chosen threshold, then output is low, and when the input is between the two levels, then output retains its value.

Schmitt trigger:

Schmitt trigger is a positive feedback comparator circuit that converts the sinusoidal input into a square wave.

The output of a Schmitt trigger circuit is always +V_CC or -V_CC

When V_NI > V_I , the output is +V_CC

When VNI < VI , the output is -VCC

Working of Schmitt trigger:

Case 1: When Vref > Vin 

V_o = +V_CC

\(V_{ref} = V_{UTP}=V_{cc}({R_2 \over R_1+R_2})\)

Case 2: When Vref < Vin 

Vo = -V_CC

\(V_{ref} =V_{LTP}= -V_{cc}({R_2 \over R_1+R_2})\)

Schmitt Trigger:

• Schmitt trigger is basically a comparator circuit with positive feedback and hence it is also called a regenerative comparator.
• When Op-Amp is positively saturated, a positive voltage is a feedback to the non-inverting input and this positive voltage holds the output in the HIGH (+Vsat) stage.
• When the output voltage is negatively saturated, a negative voltage is a feedback to the non-inverting input, holding the output in(-Vsat) LOW state.
• So, it is basically a bistable multivibrator.
• The function of the Schmitt trigger is to convert any regular or irregular-shaped input waveform into a square wave output voltage or pulse.
• If we have provided sinusoidal as input to the Schmitt trigger then it gives a square wave at the output side.

​

Additional Information

• Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the non-inverting input of a comparator or differential amplifier.
• It is an active circuit which converts an analog input signal to a digital output signal.
• The circuit is named a "trigger" because the output retains its value until the input changes sufficiently to trigger a change.
• In the non-inverting configuration, when the input is higher than a chosen threshold, then output is high.
• When the input is below a different (lower) chosen threshold, then output is low, and when the input is between the two levels, then output retains its value.
• This dual threshold action is called hysteresis and implies that the schmitt trigger possesses memory and can act as a bistable multivibrator (latch or flip-flop).
• Schmitt trigger devices are typically used in signal conditioning applications to remove noise from signals used in digital circuits, particularly mechanical contact bounce in switches.
• They are also used in closed loop negative feedback configurations to implement relaxation oscillators, used in function generators and switching power supplies.
• Note that, the Schmitt trigger can also be used with a current source to produce a sawtooth or triangle wave.

Schmitt trigger:

• Schmitt trigger is a comparator circuit with a hysteresis effect implemented by applying positive feedback to the non-inverting input of a comparator or differential amplifier.
• It is an active circuit that converts an analog input signal to a digital output signal.
• When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called hysteresis.
• The Schmitt trigger possesses memory and can act as a bistable multivibrator.
• It is called the transfer characteristics of the Schmitt trigger.

Hall Effect: When a current-carrying conductor is placed perpendicular to the magnetic field, then an Electric field is produced, which is perpendicular to both.

Concept:

The input voltage Vi changes the state of output therefore it exceeds its voltage level above a certain value called upper and lower threshold voltages.

The upper threshold point:

\({V_{UTP}} = {V_R} \times \frac{{{R_1}}}{{{R_1} + {R_2}}} + {V_0}\frac{{{R_2}}}{{{R_1} + {R_2}}}\)

Lower threshold point:

\({V_{LTP}} = {V_R}\frac{{{R_1}}}{{{R_1} + {R_2}}} - {V_0}\;\frac{{{R_2}}}{{{R_1} + {R_2}}}\)

Now, VH = VUTP - VLTP (hysteresis voltage)

Calculation:

Hysteresis Voltage

VH = VUTP - VLTP = 12 - 8 = 4 V

Additional Information

• Schmitt trigger is a comparator circuit with a hysteresis effect implemented by applying positive feedback to the non-inverting input of a comparator or differential amplifier.
• It is an active circuit that converts an analog input signal to a digital output signal.
• When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called hysteresis.
• The Schmitt trigger possesses memory and can act as a bistable multivibrator.
• It is called the transfer characteristics of the Schmitt trigger.

Schmitt trigger:

Schmitt trigger is a positive feedback comparator circuit that converts the sinusoidal input into a square wave.

The output of a Schmitt trigger circuit is always +V_CC or -V_CC

When V_NI > V_I , the output is +V_CC

When VNI < VI , the output is -VCC

Working of Schmitt trigger:

Case 1: When Vref > Vin 

V_o = +V_CC

\(V_{ref} = V_{UTP}=V_{cc}({R_2 \over R_1+R_2})\)

Case 2: When Vref < Vin 

Vo = -V_CC

\(V_{ref} =V_{LTP}= -V_{cc}({R_2 \over R_1+R_2})\)

Concept:

The input voltage V_i changes the state of output therefore it exceeds its voltage level above a certain value called upper and lower threshold voltages.

The upper threshold point:

\({V_{UTP}} = {V_R} \times \frac{{{R_1}}}{{{R_1} + {R_2}}} + {V_0}\frac{{{R_2}}}{{{R_1} + {R_2}}}\)

Lower threshold point:

\({V_{LTP}} = {V_R}\frac{{{R_1}}}{{{R_1} + {R_2}}} - {V_0}\;\frac{{{R_2}}}{{{R_1} + {R_2}}}\)

Now, V_H = V_UTP - V_LTP (hysteresis voltage)

Calculation:

In Schmitt trigger, Zener diode voltage v_d = 0.7 V

Threshold voltage V₁ = 0

Hysteresis voltage V_H = 0.2 V

\(\Rightarrow {V_H} = {V_R}\frac{{{R_1}}}{{{R_1} + {R_2}}} + {V_0}\frac{{{R_2}}}{{{R_1} + {R_2}}} - \left( {{V_R}\frac{{{R_1}}}{{{R_1} + {R_2}}} - {V_0}\frac{{{R_2}}}{{{R_1} + {R_2}}}} \right)\)

\(\Rightarrow {V_H} = 2\;{V_0}\frac{{{R_2}}}{{{R_1} + {R_2}}}\)

Now, V₀ = V_Z + V_D = 0.7 + 6 = 6.7 V

\( \Rightarrow 0.2 = 2 \times 6.7 \times \frac{1}{{1 + \frac{{{R_1}}}{{{R_2}}}}}\)

\( \Rightarrow 1 + \frac{{{R_1}}}{{{R_2}}} = 67\)

\(\Rightarrow \frac{{{R_1}}}{{{R_2}}} = 66\)

Now, (threshold) \({V_1} = {V_R} \times \frac{{{R_1}}}{{{R_1} + {R_2}}} + {V_0} \times \frac{{{R_2}}}{{{R_1} + {R_2}}}\)

\(\Rightarrow 0 = {V_R}\frac{1}{{1 + \frac{{{R_2}}}{{{R_1}}}}} + {V_0}\frac{1}{{1 + \frac{{{R_1}}}{{{R_2}}}}}\)

\( \Rightarrow {V_2} \times \frac{1}{{1 + \frac{1}{{66}}}} = - 6.7 \times \frac{1}{{1 + 66}}\)

\(\Rightarrow {V_R} = \; - 6.7 \times \frac{1}{6} = - 0.10\;V\)

Schmitt Trigger:

• It is a comparator circuit with positive feedback.
• It is a Bi-stable circuit, having two stable states (+Vsat and -Vsat).
• In this, the input sine-wave is converted to an ​asymmetrical square wave or rectangular wave. 
• The output voltage changes its states whenever the input voltage exceeds certain voltage levels (i.e. VUT & VLT)

The output waveform for a sinusoidal input is a rectangular wave.

Given:

High output voltage level = 5 V

Lower threshold voltage = 1.6 V

Upper threshold voltage = 2.4 V

Resistance (R) = 10 kΩ 

Capacitance (C) = 47 nF

t₁ = Capacitor charging time

t₂ = Capacitor discharging time

Capacitor charging diagram is given as:

In case of charging voltage across capacitor V_c(t) is given as:

V_c(t) = V_cf + (V_ci - V_cf) e^-t/RC

Where V_cf = Final value of voltage across capacitor (= 5 V)

V_ci = Initial value of voltage across capacitor (= 1.6 V)

In case of discharging voltage across capacitor V_c(t) is given as:

V_c(t) = V_ci e^-t/RC

RC = 10 × 10³ × 47 × 10^-9 = 470 × 10^-6

At the end of charging time (t₁), voltage across capacitor is = 2.4 V

V_c(t) = 2.4 = 5 + (1.6 - 5) e^{-t₁/(470 ×} 10^-6)

t₁ = 126.1 × 10^-6 s

At the end of discharging time (t₂), voltage across capacitor is = 1.6 V

V_c(t) = 1.6 = 2.4 e^{-t₂/(470 ×} 10^-6)

t₂ = 190.57 × 10^-6 s

T = t₁ + t₂ = 126.1 × 10^-6 + 190.57 × 10^-6 = 316.67 × 10^-6 s

Frequency = 1/T = 1/(316.67 × 10^-6) = 3157.87 Hz

Schmitt Trigger:

• It is a comparator circuit with positive feedback.
• It is a Bi-stable circuit, having two stable states (+Vsat and -Vsat).
• In this, input sine-wave is converted to a square wave
• The output voltage changes its states whenever the input voltage exceeds certain voltage levels (i.e. VUT & VLT)

\({v_0} = {A_{0L}} \cdot {V_d} = {A_{OL}}\left( {{v_f} - {v_{in}}} \right)\)

∴ The input sine-wave converted into a square wave

Concept:

When V_IN is active and V_REF = 0, the circuit is drawn as:

\({V_{OUT1}} = - \frac{{{R_F}}}{{{R_{IN}}}}{V_{IN}}\)  

When V_IN = 0 and V_REF is active, the circuit is drawn as:

\({V_{OU{T_2}}} = \left( {\frac{{{V_{REF}} \times {R_2}}}{{{R_1} + {R_2}}}} \right)\left( {1 + \frac{{{R_F}}}{{{R_{IN}}}}} \right)\)

Total V_out = V_out1 + V_out2

\({V_{out}} = \left( {\frac{{{V_{REF}} \times {R_2}}}{{{R_1} + {R_2}}}} \right)\left( {1 + \frac{{{R_F}}}{{{R_{IN}}}}} \right) - \frac{{{R_E}}}{{{R_{IN}}}}\;{V_{IN}}\)

Given V_REF is fixed then V⁺ is fixed, i.e.

\({V^ + } = \frac{{{V_{REF}} \times {R_2}}}{{{R_1} + {R_2}}}\)

\({V_{OUT}} = \left( {1 + \frac{{{R_F}}}{{{R_{IN}}}}} \right)\left( {\frac{{{V_{REF}}\;{R_2}}}{{{R_1} + {R_2}}}} \right) - \frac{{{R_F}}}{{{R_{IN}}}}{V_{IN}}\)

For V_IN = 0.1 V, we have V_OUT = 1 V

\(1 = \left( {1 + \frac{{{R_F}}}{{{R_{IN}}}}} \right)\left( {\frac{{{V_{REF}}\;{R_2}}}{{{R_1} + {R_2}}}} \right) - \frac{{{R_F}}}{{{R_{IN}}}}\left( {0.1} \right)\)        ---(i)

For V_IN = 10 V, we have V_OUT = 6 V

\(6 = \left( {1 + \frac{{{R_F}}}{{{R_{IN}}}}} \right)\left( {\frac{{{V_{REF}}\;{R_2}}}{{{R_1} + {R_2}}}} \right) - \frac{{{R_F}}}{{{R_{IN}}}}\left( 1 \right)\)      ---(ii)

From (i)

\(\left( {1 + \frac{{{R_F}}}{{{R_{IN}}}}} \right)\left( {\frac{{{V_{REF}} \cdot {R_2}}}{{{R_1} + {R_2}}}} \right) = 1 + \frac{{{R_F}}}{{{R_{IN}}}}\left( {0.1} \right)\)

Putting above value in eq (ii)

\(6 = 1 + \frac{{{R_F}}}{{{R_{IN}}}}\left( {0.1} \right) - \frac{{{R_F}}}{{{R_{IN}}}}\left( 1 \right)\)

\(5 = \frac{{{R_F}}}{{{R_{IN}}}}\left( { - 0.9} \right)\)

\(\frac{{{R_F}}}{{{R_{IN}}}} = - \frac{5}{{0.9}} = - 5.55\)

Since only positive values are given in the options:

\(\frac{{{R_F}}}{{{R_{IN}}}} = 5.55\)

Schmitt trigger acts as a comparator when the input voltage is greater than UTP then the output will change from –V_sat to +V_sat.

Schmitt Trigger:

• It is a comparator circuit with positive feedback.
• It is a Bi-stable circuit, having two stable states (+Vsat and -Vsat).
• In this, input sine-wave is converted to a square wave
• The output voltage changes its states whenever the input voltage exceeds certain voltage levels (i.e. VUT & VLT)

\({v_0} = {A_{0L}} \cdot {V_d} = {A_{OL}}\left( {{v_f} - {v_{in}}} \right)\)

∴ The input sine-wave converted into a square wave