Square wave generator
A square-wave generator is an electronic circuit for generating a rectangular vibration (see square wave ). The term is used both for devices and for circuit parts or electronic assemblies. Square wave generators belong to the group of signal generators .
features
Square-wave generators are characterized by the following features:
- Frequency or period and its constancy (see also jitter )
- Duty cycle (engl. Duty cycle , often adjustable or variable)
- Edge steepness ; For measuring purposes and in digital circuits, rise and fall times in the sub-nanosecond range are often required
- Upper and lower level (with laboratory devices often independently adjustable, with digital circuits ideally the ground and operating voltage level).
- For laboratory devices, the output resistance or the source impedance (often 50 ohms in order to be able to transmit the square-wave signal with low distortion via coaxial lines )
application
- Laboratory equipment
- Supply of analog and digital circuits for test purposes
- Generation of pulse trains with defined frequency, levels and duty cycle
- Adjustment of frequency response-compensated voltage dividers in probes
- Electronic circuits (examples)
- Part of sensors, switching regulators and switched-mode power supplies for displaying, regulating or changing an analog variable (e.g. temperature, output voltage, illuminance ) based on the frequency or the duty cycle
- mostly quartz-controlled clock generator for quartz watches , processors and microcontrollers (see quartz oscillator )
- Signal generators for optical or acoustic displays
- Pulse generators u. a. in radars and laser range finders
example
The adjacent circuit is a square wave generator ( tilting oscillator , astable multivibrator ) for frequencies in the range from about 0.1 Hz to 500 kHz. The generated frequency is about 1% stable and can be varied widely by selecting C and R or with the potentiometer. The circuit works with the NE555 module . The function can be described as follows: As long as the voltage on capacitor C is less than 2/3 (66%) of the operating voltage, it is charged via R (series connection of potentiometer and 1 kOhm resistor). The output voltage at pin 3 is approximately the operating voltage during this time. If the 66% value is exceeded, an internal flip-flop tips over, the output voltage drops to 0 volts and the capacitor is discharged via R. As soon as the operating voltage falls below 1/3 (33%), the flip-flop flips into its original position and the process starts over. The voltage across the capacitor is approximately in the shape of a triangle .
With a potentiometer of 20 kOhm the generated frequency can be changed in a ratio of about 1:20. It is inversely proportional to the capacitance C and R. The NE555 provides the switching thresholds of 1/3 and 2/3 internally with a voltage divider made up of three resistors. One of the connection points is brought out (pin 5). By changing the voltage on pin 5 (not connected: 2/3 of the operating voltage), the frequency can be changed electronically ( voltage controlled oscillator ). A frequency modulation can be achieved using an alternating voltage at this connection (" Kojak siren").