RC Low-Pass Filter Bode Plot: Circuit, Measurements and Online Simulator

To build this RC Low-Pass Filter Bode Plot circuit you need a function generator, a bode plotter, a 1 kΩ resistor and a 100 nF ceramic capacitor. A 1 kΩ / 100 nF low-pass filter on the Bode plotter: flat, then falling at 20 dB per decade past its −3 dB corner at 1.59 kHz, with the phase heading to −90°. Make the 6 connections in the wiring table, press Run, and and read the corner frequency off the plotter. Turn the CURSOR knob to 1.59 kHz: −3 dB and −45°. Swap R and C to make a high-pass and watch the plot flip.

Open this circuit in the free Electronics bench simulator

Parts list

Qty	Part	What it does
1	Function Generator	Sine, square, triangle or sawtooth from 1 Hz to 100 kHz, into a 50 Ω output. COM is earth. Watch it on the oscilloscope.
1	Bode Plotter	Plots a circuit's frequency response — gain in dB and phase — from 1 Hz to 1 MHz, with the −3 dB corner marked. Wire IN to the circuit's input (the function generator drives it), OUT to its output, GND to ground.
1	1 kΩ resistor	Limits current. 220 Ω in series with an LED; 10 kΩ as a pull-up or pull-down.
1	100 nF ceramic capacitor	Stores charge; blocks DC, passes AC. With a resistor it sets a time constant τ = RC (1 kΩ × 1 µF = 1 ms). Not polarised.

Wiring

#	From	To
1	Function Generator OUT	1 kΩ resistor leg 1
2	1 kΩ resistor leg 2	100 nF ceramic capacitor 1
3	100 nF ceramic capacitor 2	Function Generator COM
4	Function Generator OUT	Bode Plotter IN
5	100 nF ceramic capacitor 1	Bode Plotter OUT
6	Function Generator COM	Bode Plotter GND

Step by step

Open the electronics bench. Open the BitForBytes Embedded Lab in your browser. A circuit with no microcontroller runs on the analog bench: no install or account is needed.
Add the parts. Add a function generator, a bode plotter, a 1 kΩ resistor and a 100 nF ceramic capacitor from the parts palette (Instruments, Power, Passive and Semiconductors).
Wire 1. Connect Function Generator OUT to 1 kΩ resistor leg 1.
Wire 2. Connect 1 kΩ resistor leg 2 to 100 nF ceramic capacitor 1.
Wire 3. Connect 100 nF ceramic capacitor 2 to Function Generator COM.
Wire 4. Connect Function Generator OUT to Bode Plotter IN.
Wire 5. Connect 100 nF ceramic capacitor 1 to Bode Plotter OUT.
Wire 6. Connect Function Generator COM to Bode Plotter GND.
Run and measure. Press Run and read the corner frequency off the plotter. Turn the CURSOR knob to 1.59 kHz: −3 dB and −45°. Swap R and C to make a high-pass and watch the plot flip.

Lab sheet

// Electronics bench: Bode plot of a first-order low-pass filter
//
// fc = 1 / (2π · R · C) = 1 / (2π × 1 kΩ × 100 nF) = 1.59 kHz.
// Below fc the capacitor barely loads the output (0 dB); above it, every
// tenfold rise in frequency cuts the output tenfold (−20 dB/decade).
// At fc the output is 1/√2 of the input (−3 dB) and lags it by 45°.
//
// The plotter runs an AC small-signal analysis, the way SPICE does.

What to try

Press Run and read the corner frequency off the plotter. Turn the CURSOR knob to 1.59 kHz: −3 dB and −45°. Swap R and C to make a high-pass and watch the plot flip.

Frequently asked questions

How do I wire the RC Low-Pass Filter Bode Plot circuit?

Make 6 connections: Function Generator OUT to 1 kΩ resistor leg 1; 1 kΩ resistor leg 2 to 100 nF ceramic capacitor 1; 100 nF ceramic capacitor 2 to Function Generator COM; Function Generator OUT to Bode Plotter IN; 100 nF ceramic capacitor 1 to Bode Plotter OUT; Function Generator COM to Bode Plotter GND.

What parts do I need for the RC Low-Pass Filter Bode Plot?

A function generator, a bode plotter, a 1 kΩ resistor and a 100 nF ceramic capacitor.

Can I simulate the RC Low-Pass Filter Bode Plot online for free?

Yes. The BitForBytes Embedded Lab solves the circuit in time, the way SPICE does (nodal analysis with real diode, transistor and capacitor models), and gives you a bench power supply, function generator, oscilloscope and multimeter to measure it — free, in the browser.

What does this circuit show?

A 1 kΩ / 100 nF low-pass filter on the Bode plotter: flat, then falling at 20 dB per decade past its −3 dB corner at 1.59 kHz, with the phase heading to −90°.