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Op-Amp Series – Part 7: The Differentiator Amplifier

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The Differentiator Amplifier Final Build A differentiator amplifier is an operational amplifier circuit that produces an output proportional to the rate of change of the input signal. Instead of amplifying the voltage itself, it amplifies how fast the voltage is changing. In simple mathematical terms: Vout = -RC × (dVin/dt) This means: If the input changes slowly → small output If the input changes quickly → large output If the input is constant (DC) → output is zero Why is that powerful? Because many real-world systems care about change, not steady values. The Basic Differentiator Circuit Basic Circuit A basic differentiator uses: One capacitor One resistor One op-amp Key layout: Capacitor in series with the input Resistor in the feedback path Non-inverting input connected to ground This is almost the reverse of the integrator circuit. How the Circuit Works Let’s break it down conceptually. The capacitor allows current to flow only when the input voltage is changing. The faster the ...
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Op-Amp Series – Part 6: The Integrator Amplifier

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The Integrator Amplifier The integrator amplifier  is an operational amplifier circuit that performs a mathematical integration  of the input signal.  Unlike the previous amplifier circuits, the output of an integrator doesn’t simply scale or invert the input. Instead, it accumulates the input over time , producing an output voltage proportional to the area under the input waveform . Integrator circuits are widely used in: Signal processing Waveform generation Analog computing Control systems Audio and synth circuits We’ll start with the theory and maths, then build a real, working integrator on the bench using an LM358. What Is an Integrator Amplifier? An integrator is a modified inverting op-amp circuit where the feedback resistor is replaced with a capacitor . This can be seen in the circuit below. Integrator Amplifier Circuit The basic circuit consists of the following: - Input resistor: R Feedback capacitor: C Non-inverting input tied to ground Output fed...
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Op-Amp Series – Part 5: The Differential Amplifier

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  The Differential Amplifier A differential amplifier is an operational amplifier circuit that amplifies the difference between two input voltages . Instead of measuring a signal relative to ground, it measures how much one signal differs from another . This makes differential amplifiers incredibly useful for: Rejecting noise Comparing signals Sensor interfaces Audio and measurement circuits In simple mathematical terms: Output = (Input 1 – Input 2) × Gain In the real world, signals are often noisy. Long wires, motors, power supplies, and digital circuits can all introduce interference. A differential amplifier helps by: Amplifying only the difference between inputs Rejecting signals that appear equally on both inputs (called common-mode signals ) The Basic Differential Amplifier Circuit Differential Amplifier Circuit A classic differential amplifier uses four resistors and one op-amp. For proper operation: Resistor ratios must match This ensures accurate subtract...
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Op-Amp Series – Part 4: The Summing Amplifier

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The Summing Amplifier In this part of the op-amp series, we’re going to build and test summing amplifiers . A summing amplifier combines multiple input signals into one output , making it one of the most useful and flexible op-amp building blocks. In this post we will: Build two types of summing amplifier Measure real voltages on the bench Match the math directly to what we measure Highlight practical limitations with single-supply op-amps What Is a Summing Amplifier? A summing amplifier is an op-amp circuit that adds multiple input signals together and produces a single output voltage. Key idea (very important): 👉 Summing amplifiers add currents , not voltages. 👉 The op-amp output converts the summed current back into a voltage. Each input voltage is converted into a current by a resistor. Those currents are summed at the op-amp input and converted back into a voltage at the output. There are two basic types of summing amplifiers: - Inverting Non-Inverting Type 1 — Inverti...
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