A function generator produces electrical signals (sine waves, square waves, and others) that you feed into a circuit to test how it responds. Using one comes down to three things: selecting a waveform shape, dialing in the frequency and amplitude you need, and connecting the output to your circuit or oscilloscope with the right cable. Once you understand the core controls, the process is straightforward regardless of which model sits on your bench.
The Three Core Controls
Every function generator, whether analog or digital, has the same fundamental parameters you’ll adjust for nearly every task.
Frequency sets how many cycles of the waveform occur each second, measured in hertz (Hz). A 1,000 Hz signal completes one thousand full cycles per second. You’ll typically see a frequency knob or button, sometimes paired with a range multiplier. On digital models, you press the Freq button and type in a value, then select units (Hz, kHz, MHz).
Amplitude controls how tall the signal is, measured in volts. Most generators display this as peak-to-peak voltage (abbreviated Vpp), which is the total distance from the lowest point of the waveform to the highest. A 5 Vpp sine wave swings from +2.5 V to −2.5 V. Typical benchtop generators output anywhere from 25 millivolts up to about 5 volts into a standard load, so you’re working with relatively low power levels.
DC offset shifts the entire waveform up or down from zero. Without an offset, a sine wave is centered on 0 V, spending equal time in positive and negative territory. Adding a 2.5 V offset to a 5 Vpp square wave, for example, shifts it so it swings between 0 V and 5 V instead of between −2.5 V and +2.5 V. This is useful when your circuit expects only positive voltages, like most digital logic.
Waveform Types and When to Use Them
Most function generators offer at least four standard waveform shapes, and each one serves a different purpose in circuit testing.
- Sine wave: The most common starting point. Sine waves contain only a single frequency, making them ideal for testing amplifier gain, measuring filter response, and checking audio circuits. If you need a clean, predictable signal, start here.
- Square wave: Jumps abruptly between a high and low voltage. Square waves are perfect for testing digital circuits, checking how a circuit responds to sudden voltage changes, and simulating clock signals. Because the sharp edges contain many higher-frequency components, a square wave also reveals how well a circuit handles fast transitions.
- Triangle and ramp waves: Rise and fall in straight lines rather than curves. Triangle waves climb and descend at equal rates, while ramp (sawtooth) waves rise gradually and drop sharply, or vice versa. These are useful for testing linear sweep circuits and driving certain types of modulators.
- Pulse: Similar to a square wave but with an adjustable duty cycle, meaning you can control how long the signal stays high versus low. Pulse signals provide precise timing sources for synchronizing amplifiers, communications systems, and radar equipment.
Higher-end generators also offer an arbitrary waveform mode, where you can program a custom shape. For most bench work, though, the four standard waveforms cover what you need.
Step-by-Step Setup
Here’s the general process that applies to virtually any function generator, analog or digital.
First, power on the unit. Digital generators take a few seconds to run internal self-tests before they’re ready. Analog models are available immediately. Don’t connect it to your circuit yet.
Next, select your waveform. On an analog generator, this is usually a physical switch with icons showing a sine curve, square wave, and triangle. On a digital model, look for a Function menu or dedicated waveform buttons. Choose sine if you’re just getting started or verifying your setup.
Now set the frequency. A good default for initial testing is 1 kHz. On analog models, turn the frequency knob and set the range multiplier so the combination gives you 1,000 Hz. On digital models, press the Freq button, type “1,” and select kHz as the unit.
Set the amplitude. For a safe starting point, try 2 Vpp or lower. On an analog generator, the amplitude knob at roughly the 12 o’clock position with any attenuator switches at 0 dB gives you a moderate output. On digital models, press the Ampl button and key in your desired voltage.
Adjust the DC offset if your application requires it. For most basic testing, leave this at 0 V.
Finally, enable the output. This is a step people often miss: many digital generators won’t send any signal until you press a dedicated Output button, even after you’ve configured everything. Look for this button near the output connector on the front panel. Until you press it, the BNC connector is inactive.
Connecting to Your Circuit or Oscilloscope
Function generators use BNC connectors for their output, and the standard cable for bench work is a BNC-to-BNC coaxial cable (typically RG58, which has 50-ohm impedance). To view your signal on an oscilloscope, run a BNC cable from the generator’s main output to one of the oscilloscope’s input channels.
One thing to understand about these cables: function generators are designed to work into a 50-ohm load. When you connect to an oscilloscope, the scope’s input impedance is usually 1 megohm, not 50 ohms. This mismatch is fine for most low-frequency work, but it means the voltage you see on the oscilloscope will be roughly double what the generator’s display shows, because the generator assumes half the voltage drops across an internal 50-ohm source resistance and half across a matched 50-ohm load. When the load is effectively infinite (1 megohm), almost all the voltage reaches the scope.
If you need accurate voltage levels at higher frequencies, or if you see ringing and signal distortion, place a 50-ohm BNC terminator at the oscilloscope input. This small inline adapter contains a 50-ohm resistor that properly terminates the cable and absorbs reflections that would otherwise distort your signal. For frequencies below a few hundred kilohertz with short cables, you can usually skip this and just mentally account for the voltage doubling.
Grounding and Safety
The outer shell of a BNC connector is connected to the generator’s ground, which is tied to earth ground through the power cord. The oscilloscope’s BNC shell is also earth-grounded. This means the ground clips and outer conductors of both instruments are electrically connected through the building’s wiring, whether or not you run a cable between them.
This shared ground creates a risk when you’re measuring a component that isn’t referenced to ground. If you clip the oscilloscope’s ground lead to a point in your circuit that sits at some voltage above ground, you create a short circuit through the ground wires of both instruments. This can damage your equipment, blow fuses, or in serious cases create a shock or fire hazard.
The safe approach: always connect ground clips to the actual ground node in your circuit. Never defeat the grounding system of your oscilloscope by removing the ground prong from the power plug or using an isolation transformer to “float” the instrument. Tektronix specifically warns that this practice causes cumulative stress on the oscilloscope’s internal insulation, which can lead to dangerous failures later, even after you return to normal grounded operation. If you genuinely need to measure voltage across a non-grounded component, use a differential probe instead.
Troubleshooting Common Problems
If you see no signal on the oscilloscope, the most likely cause is that the generator’s output is not enabled. Press the Output button on the generator and check for an indicator light confirming the output is active.
If the signal appears but the amplitude is wrong, check whether the generator expects a 50-ohm load while you’re connected to a high-impedance input. Many generators have a menu setting to toggle between 50-ohm and high-impedance output modes. Switching to high-impedance mode tells the generator to adjust its displayed voltage to match what you’ll actually see.
If the waveform looks distorted, particularly if square wave edges look rounded or overshoot badly, the oscilloscope’s bandwidth may be too low for the signal’s frequency, or you may need a 50-ohm terminator to eliminate cable reflections. Try reducing the frequency to see if the shape improves.
If you hear a relay click but the signal cuts out intermittently, the BNC cable or connector may have a loose connection. Wiggle the cable at both ends. BNC connectors lock with a quarter-turn bayonet mechanism; make sure you push in and twist until the connector clicks into place rather than just pushing it on loosely.