diff --git a/opamp-basics.iapresenter/assets/ideal.png b/opamp-basics.iapresenter/assets/ideal.png new file mode 100644 index 0000000..7a02151 Binary files /dev/null and b/opamp-basics.iapresenter/assets/ideal.png differ diff --git a/opamp-basics.iapresenter/info.json b/opamp-basics.iapresenter/info.json new file mode 100644 index 0000000..333ce0a --- /dev/null +++ b/opamp-basics.iapresenter/info.json @@ -0,0 +1,9 @@ +{ + "creatorIdentifier" : "net.ia.presenter", + "net.ia.presenter" : { + "localFileIdentifier" : "5D0017B0-9C16-4EE2-947E-26C4963CC3C5" + }, + "transient" : false, + "type" : "net.daringfireball.markdown", + "version" : 2 +} \ No newline at end of file diff --git a/opamp-basics.iapresenter/text.md b/opamp-basics.iapresenter/text.md new file mode 100644 index 0000000..0a4ccb5 --- /dev/null +++ b/opamp-basics.iapresenter/text.md @@ -0,0 +1,158 @@ +# Opamps Design +--- + +# Basic Op-Amp Design + Op-amp fundamentals: ideal model, negative feedback, and open-loop behavior + +Welcome! These slides introduce the op-amp abstraction you'll use in analog design, including the ideal model, the actual operation of negative feedback, and why open-loop operation saturates. +--- + +## Ideal Op-Amp: Model + Open-loop gain: $v_{out} = A (v_+ - v_-)$ + Ideal assumptions: + • $A \to \infty$ + • Input currents: $i_+ = i_- = 0$ + • Output can source/sink as needed (within rails) + • Infinite input impedance, zero output impedance + +The “ideal” device is an amplifier with huge differential gain. In practice, $A$ is large but finite and bandwidth-limited. Keep these as design heuristics (“golden rules”). + +--- + +## Ideal opamp +/assets/ideal.png +size: contain +--- + +## Golden Rules (with Negative Feedback) + 1) No input current: $i_+ = i_- = 0$ + 2) With negative feedback in linear region: $v_+ \approx v_-$ + +When negative feedback closes the loop and the output is not saturated, the amplifier forces the differential input toward zero. + +--- + +## Open-Loop vs Closed-Loop + Open-loop: + • Tiny differential input → huge $v_{out}$ + • Output rails → saturation + Closed-loop (with feedback): + • Gain set by resistors/network + • Stable, predictable behavior + +Open-loop op-amps act like comparators (saturate high/low). Design uses closed-loop topologies to set usable gain/bandwidth. + +--- + +## Inverting Amplifier + Topology: + • Input $v_{in}$ → $R_{in}$ → (−) node + • Feedback $R_f$ from $v_{out}$ to (−) + • (+) tied to reference (usually ground) + + Result (ideal): + $G = \dfrac{v_{out}}{v_{in}} = -\dfrac{R_f}{R_{in}}$ + +Speaker notes: +Kirchhoff at the inverting node: no current into op-amp, so $(v_{in}-v_-)/R_{in} + (v_{out}-v_-)/R_f = 0$. +With negative feedback in linear region $v_- \approx v_+ = 0$, giving $v_{out} = -\dfrac{R_f}{R_{in}} v_{in}$. + +--- + +## Non-Inverting Amplifier + Topology: + • (+) sees $v_{in}$ + • Divider from $v_{out}$: $R_f$ to output, $R_g$ to ground into (−) + + Result (ideal): + $G = \dfrac{v_{out}}{v_{in}} = 1 + \dfrac{R_f}{R_g}$ + +Speaker notes: +Use $v_- \approx v_+ = v_{in}$. The divider forces $v_- = v_{out}\dfrac{R_g}{R_f+R_g}$. Solve for $v_{out}$. + +--- + +## Voltage Follower (Buffer) + Topology: + • Non-inverting with $R_f \to \infty, R_g \to \infty$ (direct feedback) + • (+) = input, (−) = output + + Ideal result: + $G = 1 \quad\text{and}\quad Z_{in}\to\infty$ + +Provides isolation: high input impedance, low output impedance. + +--- + +## Summing (Inverting) Amplifier + Multiple inputs $v_{1..n}$ via $R_{1..n}$ into (−); feedback $R_f$. + + Ideal result: + $v_{out} = -R_f\left(\dfrac{v_1}{R_1}+\dfrac{v_2}{R_2}+\cdots+\dfrac{v_n}{R_n}\right)$ + +Great for weighted sums and simple DACs. + +--- + +## Negative Feedback Intuition + • Senses output error and drives $v_+ - v_- \to 0$ + • Sets closed-loop gain via passive network + • Improves linearity and reduces sensitivity to op-amp $A$ + +Speaker notes: +As long as the op-amp isn’t saturating and has sufficient phase margin, the loop stabilizes with $v_+ \approx v_-$. + +--- + +## Open-Loop Behavior (Comparator-like) + With no feedback: + • $A$ is huge ⇒ sign of $(v_+ - v_-)$ decides the rail + • Output saturates near $+V_{rail}$ or $-V_{rail}$ + • Not for linear amplification + +Use a proper comparator IC for clean switching; many op-amps are slow or have input structures unsuited to rail-to-rail comparison. + +--- + +## Practical Limits (Reality Check) + Non-idealities: + • Finite $A(s)$, finite bandwidth (GBW) + • Input bias currents & offsets + • Slew rate limits + • Output swing vs rails & load + +Design with datasheet limits; verify stability with phase margin and consider source/load impedance. + +--- + +## Quick Design Examples + Inverting: Target $G=-10$ ⇒ pick $R_{in}=10\,\text{k}\Omega$, $R_f=100\,\text{k}\Omega$ + Non-inverting: Target $G=11$ ⇒ $R_f/R_g=10$ ⇒ $R_f=100\,\text{k}\Omega, R_g=10\,\text{k}\Omega$ + +Speaker notes: +Choose E-series values; check input/output swing vs rails and bandwidth: $f_{-3\text{dB}}\approx \dfrac{\text{GBW}}{G}$. + +--- + +## Where Each Topology Shines + Inverting: + • Precise gains, easy summing, virtual ground node + Non-inverting: + • High input impedance, sensor buffering + Follower: + • Isolation between stages + +Pick based on source impedance and required gain. + +--- + +## Wrap-Up + • Ideal rules simplify analysis + • Negative feedback sets the gain and linear region + • Open-loop op-amps saturate—use comparators for switching + +Thank you! Questions? + + + + diff --git a/opamp-basics.iapresenter/thumb.png b/opamp-basics.iapresenter/thumb.png new file mode 100644 index 0000000..c67d418 Binary files /dev/null and b/opamp-basics.iapresenter/thumb.png differ