WAVEFORM GENERATOR
SINEWAVE GENERATOR , MULTIVIBRATOR AND TRIANGULAR WAVE
GENERATOR
SQUARE WAVE GENERATOR USING OP-AMP (
ASTABLE MULTI VIBRATOR)
Goal of the Circuit:
• to produce a square wave (alternating high and low voltage) continuously,
without any external trigger — purely self-driven oscillation.
Circuit overview:
• Main Components:
• Op-Amp (like LM741)
• Resistors R1 & R2: voltage divider (sets threshold voltage)
• Capacitor C: controls timing (how fast it charges/discharges)
• Power Supply: ±V for op-amp (example: ±12V)
Circuit connections
• Non-inverting input (+) connects to a voltage divider made using R1 and R2
from the output .
• Inverting input (–) connects to the junction between the op-amp output and the
capacitor C . The other end of C is grounded .
• The output of the op-amp swings between +Vsat and –Vsat (near supply
limits).
4. DETAILED WORKING (STEP-BY-STEP)
Initial State:
• Let’s say the output starts at +Vsat (positive saturation).
• This +Vsat is divided through R1 and R2 and appears at the non-inverting
input (+).
• The capacitor C starts charging toward +Vsat through the op-amp’s output.
While Charging:
• The voltage at inverting input (–) slowly increases as the capacitor charges.
• At some point, V– becomes slightly greater than V+.
• The op-amp switches output from +Vsat to –Vsat because it amplifies the
difference.
Discharge Begins:
• Now the output is –Vsat.
• This reverses the charging direction — capacitor now starts charging toward –Vsat.
• The voltage at the inverting input (–) starts to drop.
• Second Switch:
• Eventually, V– drops below V+ again.The op-amp switches back to +V_sat.This
keeps happening repeatedly, generating a square wave at the output.
5. Key Principle Behind Switching:
• This works due to positive feedback through the R1–R2 voltage divider. This
feedback sets a reference threshold voltage at the non-inverting input (+), and the
capacitor at the inverting input (–) keeps crossing this threshold — making the op-
amp switch output polarity automatically.
6. Waveforms:
Output waveform:
• A perfect square wave — alternates between +Vsat and –Vsat . Capacitor
voltage: A slow triangle-like waveform (charging and discharging curve).
7. Time Period and Frequency:
• If R1 and R2 form a voltage divider, then : Let,
• beta = frac{R2}{R1 + R2}
• Then , T = 2RC \ln\left( \frac{1 + \beta}{1 - \beta} \right)f = \frac{1}{T} ]
8. Applications:
• Clock generation in digital circuits
• Tone generation , Test signal generator , LED blinkers, buzzers, square wave
sound
WAVEFORMS
1. Back-to-Back Zener Diodes
What it is:
• Two Zener diodes connected in opposite directions (anode to cathode) across a circuit
path.
Why it's used:
• To limit voltage in both directions — they conduct when the voltage exceeds their
breakdown voltage in either polarity.
Working:
• When the input voltage is within the Zener breakdown voltage, both diodes remain
non-conducting.
• When the input exceeds the breakdown voltage, one of the diodes starts conducting,
clamping the voltage.
Application:Wave shaping, clipping circuits, and over-voltage protection.
• Diagram (textual):Signal ----|<----->|---- Ground ZD1 ZD2ZD1 and ZD2
are Zener diodes facing opposite directions.
• 2. Asymmetric Square Wave Generator
What it is:
• A square wave generator where high and low durations (duty cycle) are not
equal — e.g., high for 1 ms, low for 2 ms.
How it's done:Modify the basic op-amp astable multivibrator.Use two different
resistors (R1 and R2) to control charging and discharging paths of the capacitor
differently.
Circuit concept:Place diodes in parallel with R1 and R2 to separate charge and
discharge paths.One diode allows current through R1 during charging, another
through R2 during discharging.
• Timing :T_{high} = R1 \cdot C \cdot \ln(2)T_{low} = R2 \cdot C \cdot \ln(2)
]\text{Frequency} = \frac{1}{T_{high} + T_{low}}Application:Pulse
generatorsTimer circuitsPWM signal generation
ASYMMETRIC SQUARE WAVE GENERATOR
MONOSTABLE MULTIVIBRATOR USING OP-AMP
Introduction
• • A monostable multivibrator has one stable state and one quasi-stable state.
• It stays in the stable state until triggered.
• After receiving a trigger input, it switches to the quasi-stable state for a fixed time T, and
then returns to the stable state automatically.
• Used to generate a single pulse of defined width.
2. Circuit Diagram
• Refer to textbook Fig 5.11(b) or include a simulated circuit image here.
3. Circuit Components
• • Op-Amp (comparator operation)
• R1, R2, R3: voltage divider and feedback
• C: timing capacitor
• Diodes D1, D2: protect and shape the input
• Vin: negative trigger pulse input
4. Initial Conditions (Stable State)
• • Output Vo = +V_sat
• Voltage divider (R1 and R2) sets non-inverting input to +βV_sat
• Capacitor C is fully charged
• No output pulse is generated until triggered
5. Triggering
• • A negative trigger pulse (V1) is applied to the inverting input through a
differentiator (R4–C) and diode D2
• The diode conducts momentarily, causing capacitor C to discharge, dropping
voltage at (–) input
• Now, V– < V+ → op-amp switches to –V_sat
6. Quasi-Stable State Begins
• • Vo = –V_sat
• Capacitor C starts charging toward –V_sat
• During this time, op-amp stays in quasi-stable state
• Duration of this state is the pulse width T
MONOSTABLE MULTI VIBRATOR
7. Return to Stable State
• • As capacitor charges, V– increases
• Once V– > V+ (= +βV_sat), output flips back to +V_sat
• System returns to stable state
8. Output & Capacitor Waveforms
• • Vo waveform: Pulse of width T, then returns high
• Vc waveform: Exponential ramp during output LOW
Refer to textbook Fig 5.11(c & d).
9. Pulse Width (Time Period)
• T = RC × ln((1 + β)/(1 - β))
Where:
• R and C are timing components
• β = R2 / (R1 + R2)
10. Applications
• • Timing pulses
• Pulse width modulation
• Frequency divider
• Timer in digital systems
TRIANGULAR WAVE GENERATOR USING OP-AMP
Introduction
• A triangular waveform generator produces a continuous, linear ramp-up and ramp-down voltage
waveform.
• It is widely used in signal generation, modulation, timing, and control applications.
• It works by integrating a square wave signal.
Basic Working Principle
• A square wave is generated using a comparator (A₁).
• The square wave is then integrated using an op-amp integrator (A₂) to produce a triangular wave.
• The triangular wave is fed back into the comparator to control its switching.
Circuit Diagram
• (Insert clear circuit image from the textbook or redrawn using software tools)
• Two op-amps: Comparator (A₁), Integrator (A₂)
• R₂, R₃: voltage divider for comparator threshold
• R, C: Integrator components
Circuit Components
• A₁: Comparator, generates square wave
• A₂: Integrator, outputs triangular wave
• R₂, R₃: Form reference voltage at point P
• R, C: Set the slope of the triangular waveform
• Feedback loop: Connects triangular wave to comparator input
Working – Square Wave Generation
• When A₁ output = +V_sat, it feeds the integrator
• A₂ integrates +V_sat → produces a downward slope
• Voltage at P decreases and when it crosses –threshold, A₁ switches to –V_sat
Working – Triangular Wave Generation
• A₁ switches to –V_sat, and A₂ integrates –V_sat → produces upward slope
• Voltage at P increases and when it crosses +threshold, A₁ switches again
• The cycle repeats, creating a continuous triangle waveform
• Output Waveforms
• (Insert diagram from book or draw)
• Vo (A₁ output): Square waveform
• Vo (A₂ output): Triangular waveform
• Time period = T, with symmetrical up/down ramps
• Key Equations
• Ramp voltage slope: dV/dt = ±V_sat / RC
• Time period T = 4 * V_amp * RC / V_sat
• Threshold voltage (±V_thresh) = (R₃ / (R₂ + R₃)) * V_sat
• Advantages
• Simple and low-cost design
• Frequency and amplitude can be adjusted via RC values
• Stable and repeatable waveforms
Applications
• Function generators
• Waveform synthesis
• Modulation circuits
• Sweep generators for oscilloscopes
• Analog timing circuits
CIRCUIT DIAGRAM
WAVEFORM
BASIC PRINCIPLES OF SINE WAVE OSCILLATORS
• Introduction
• Sine wave oscillators are circuits that produce continuous sinusoidal outputs without any
external input signal.
• They are essential in audio, RF, and signal generator circuits.
• They operate using positive feedback and frequency-selective networks.
• Block Diagram of Feedback Oscillator (Fig 5.14)
• Shows the basic structure of a feedback oscillator.
• Components:
• - Basic Amplifier A
• - Frequency Selective Feedback Network β
• Loop gain is Aβ
• Output voltage: vₒ = A·v₁
• Feedback voltage: v_f = β·vₒ = Aβ·v₁
• (Insert Fig. 1 diagram here)
FIG 1
Oscillation Condition — Barkhausen Criterion
• For sustained oscillations:
• 1. Magnitude condition: |Aβ| = 1
• 2. Phase condition: ∠A(ω₀)β(ω₀) = 0° or multiples of 2π
• These ensure that the feedback is constructive and reinforces the input at a
specific frequency ω₀.
Oscillation Startup (Fig 2)
• Noise (like Johnson’s noise or thermal noise) acts as the initial signal.
• If |Aβ| > 1, this small signal gets amplified repeatedly.
• Output amplitude increases exponentially.
• Oscillation begins even without an external signal.
• (Insert Fig. 2 diagram here)
FIG 2
Oscillation Growth & Saturation
• As oscillations grow, the amplifier reaches non-linear region (e.g., transistor
saturation).
• This limits the amplitude growth.
• Final waveform is a steady sine wave with constant amplitude.
Practical Design Considerations
• Exact |Aβ| = 1 is hard to maintain due to:
• - Temperature changes
• - Aging of components
• - Supply voltage drift
• Designers keep |Aβ| slightly more than 1 (about 1–5%) to ensure startup.
• Non-linearity limits amplitude and stabilizes oscillation.
