signal generators

see also:

• frequency response analyzers
• multimeters
• spectrum analyzers
• oscilloscopes
• software defined radio (SDR) receivers
• basic electronics
• DC power supplies

• signal generators generate and transmit electrical signals with varying voltages over time
• the output is usually restricted to low voltages and may have many patterns such as:
  • function generators:
    • sine wave
    • saw wave
    • square wave
    • these are used for general electronics and audio testing
  • pulses:
    • generate short-duration pulses crucial for digital, timing, and medical device assessment
  • Arbitrary Waveform Generators (AWG)
    • allow custom waveform creation for advanced R&D and unique system simulations
    • support digital electronics debugging by generating custom, precisely controlled waveforms that simulate real-world digital signals, noise, glitches, and timing scenarios that digital circuits may encounter
    • can introduce controlled jitter, glitches, or signal distortions, critical for evaluating a circuit’s tolerance to timing errors, synchronization issues, or signal integrity problems
    • by generating sequences that replicate digital communication protocols (e.g., USB, PCI-E, SATA), AWGs help verify receiver functionality, interface timing, and decoder logic
  • ECG wave
  • a previously recorded wave pattern
  • etc

• providing the input signal for frequency response analyzers
• providing the input signal for VNAs in measuring radio antenna systems
• providing input signal for testing electronic components and systems
  • testing a capacitor and determining its capacitance
    • need to ensure the signal frequency is lower than that needed to fully charge the capacitor
    • measure the resistance of a 100 Ohm resistor with a multimeter
    • set the signal generator for sine wave at 2Vpp, 1kHz connect to scope, turn on then configure scope to average to read the “open” voltage, then return back to normal mode
    • connect signal generator to each end of the resistor and connect scope probes across the resistor - set scope to average to and measure the “load” voltage which will have reduced
    • signal generator impedance = load resistance of the resistor itself x (open voltage/load voltage - 1) and this is usually around 50 Ohms
    • time constant of a capacitor = combined resistance (resistance of signal generator output impedance - usually 50 Ohm + resistance of the resistor) x capacitance and the capacitor needs 5 x time constant to fully charge (99.3%), at 1 time constant it will achieve 63.3% charge
    • hence to ascertain what frequency to use as a starting point, use the estimated capacitance in Farads in the above equation
      • ascertain time to full charge and discharge by doubling the time to fully charge (ie. this makes it 10 x time constant)
      • take the inverse of this total time to find the maximum frequency that can be used to allow full charge and discharge cycles and this may be around 5Hz
    • now place the resistor in series with the capacitor and set the signal generator o square wave at this new lower frequency and 10Vpp
    • connect the signal generator to each end of this circuit, the probe ground to it's ground, and the probe +ve to the other side of the capacitor
    • you will probably need to manually adjust scale and trigger position of the scope - eg. 2V and 20msec per division, centre signal, set scope to average and adjust cursors to measure the full charge voltage which should be your input voltage, then move the cursors to measure the time to get from 0V to 63.3% of the peak voltage and this will give you the true time constant and you can feed this back into the above equation to determine the actual capacitance
    • you can see the actual current changes by adding a shunt resistor after the capacitor (on the ground side) and a 2nd probe connected across the shunt resistor - this may need use of high resolution mode to clean up the ch2 signal
      • NB. by ascertaining the voltage across a shunt resistor, use Ohm's law to calculate the current = voltage / resistance of the shunt resistor
    • https://www.youtube.com/watch?v=LaY47Qrfs0c at ~23min
  • testing LEDs
    • use a signal gen 100Hz sine wave to a circuit with a LED and then a 10 Ohm resistor in series
    • scope Ch1 probe to ground and to +ve side of the LED and Ch2 probe to ground and +ve side of the resistor
    • https://www.youtube.com/watch?v=LaY47Qrfs0c at ~28min
• providing the carrier wave for radio transmissions
  • the signal generator outputs a stable, periodic waveform—usually a sine wave at the desired carrier frequency
  • this carrier is sent to the modulation stage, where it is combined with the message signal, altering the carrier's amplitude, frequency, or phase to encode information
  • the point where the voltage changes from 0V and starts going up is the “threshold” voltage for the LED and it will light up beyond this
  • the modulated carrier is then amplified and broadcast via an antenna as a radio wave
• providing sine waves for creating X-Y mode Lissajous patterns on the scope
  • you need two sine wave inputs to the scope (ie. 2 signal generators), start by having them both at same frequency and phase, then adjust phase of 2nd one to 90deg and you will get a circle, adjust frequency to get Australian ABC TV station patterns, etc
• providing reference signals for testing RF equipment
  • creating reference RF signals for evaluating radio receivers, transmitters, or other RF equipment
• modulation demonstrations
  • allows controlled laboratory simulation of radio communications by providing both carrier and modulating signals.
• automotive uses
  • validate in-car audio systems, sensors, and electronic control units (ECUs) by mimicking on-road and in-vehicle conditions
• audio signal tracing to test audio pre-amps
  • see https://www.youtube.com/watch?v=Vox-OEr2OfM using a tiny cheap FNIRSI DSO-510 to find the faulty transistor
    • 1kHz, 1Vpp sine wave
• Medical Device Testing
  • pulse generators test diagnostic and imaging equipment like MRI and ultrasound machines, ensuring accuracy and reliability

• maximum frequency
  • Fnirsi TSG6020 up to 60MHz, dual channel; 200 MSa/s, 14-bit Precision; 6 Modulation Types (AM/FM/PM/FSK/ASK/PSK);
  • Fnirsi DPOS350P: 0.01Hz - 50MHz for sine wave; other wave forms 3MHz/5MHz/10MHz max depending on wave form;
  • FNIRSI SG-004A Multi-functional Signal Generator: 0 - 9.999kHz and seems it can do up to 200kHz ?only square wave - three modes: monotonous rise, monotonous fall and cycle?
• frequency resolution
  • Fnirsi DPOS350P: 1Hz
• duty cycle resolution
  • duty cycle is how wide the wave form is as % of cycle
  • Fnirsi DPOS350P: 0.1%
• amplitude
  • Fnirsi DPOS350P: 0-5V PP
  • FNIRSI SG-004A Multi-functional Signal Generator: 0-24V
  • Fnirsi TSG6020: 0-20V
• amplitude resolution
  • Fnirsi DPOS350P: 1mV
• offset
  • Fnirsi DPOS350P: -2.5V ~ +2.5V
• waveform types