What is a Sawtooth Wave?

Sawtooth Wave is one of the common waveforms. The waveform of the standard sawtooth wave first rises in a straight line, then falls sharply, then rises again, and then falls sharply, and so on. It is a non-sinusoidal wave. Because it has a saw-like waveform, that is, a repeating structure with a straight diagonal line and a straight line perpendicular to the horizontal axis, it is named a sawtooth wave. ^[1]

use

A circuit that can generate a sawtooth signal periodically, also known as a scanning circuit or a time base generator. The waveform of the sawtooth voltage or current is shown in Figure 1. T is the scan period, T1 is the scan time, and T2 is the flyback time. The sawtooth voltage wave is mainly used as the scanning voltage in the oscilloscope circuit, and the sawtooth current wave is mainly used as the deflection current in the picture tube circuit.

Sawtooth wave generator atlas

The sawtooth wave generator can be divided into two types: self-excited and other-excited. The former is less stable, and modern time-base generators use the latter.
Sawtooth voltage generator: Figure 2a is a separate-excitation sawtooth voltage wave generating circuit composed of an RC charge and discharge circuit. When the input terminal is controlled by the pulse voltage u _i shown in FIG. 2 b, the transistor is equivalent to an electronic switch. When u _{i is} in the period T ₁ , the transistor is turned off, and the power supply voltage E _c charges the capacitor C through the resistor R. The output voltage u ₀ across C rises exponentially. During T ₂ , the transistor is turned on, the charge on C is discharged through it, and u ₀ drops rapidly. If T ₁ / RC << 1, that is, T ₁ occupies only a small part of the beginning of the exponential curve, then u ₀ can be approximately considered to increase linearly during T. Under the condition that E _c is constant, the larger u _m is, the worse the linearity of the scanning forward is. Generally, the charging current of C in the circuit of Fig. 2a changes exponentially, so the nonlinear coefficient is large. If you try to keep the charging current constant, the voltage u ₀ across C will increase linearly. A sawtooth wave generator with constant current source charging or capacitor negative feedback can meet this requirement ^[2] .

A sawtooth voltage generator composed of an operational amplifier. The electronic switch K is turned off within the time from 0 to T ₁ ,

The output voltage u ₀ varies linearly with time. When K is closed, u ₀ decreases rapidly with the discharge of C. As long as the switch K is opened and closed periodically, u ₀ changes according to the law of zigzag.

Sawtooth wave generator atlas

Sawtooth current generator: In the picture tube scanning circuit, the load of the sawtooth current generator is an inductor. When the operating frequency is low and the distributed capacitance of the coil can be ignored, the role of the inductive coil can be represented by the lumped inductance L _y and the lumped resistance R _y (Figure 4). The transistor T constitutes a linear current amplifier. The excitation signal voltage u _i is a sawtooth voltage wave, and the current flowing through L _y is a sawtooth current wave (Fig. 5a). 5b and c. The combined voltage waveform u _{y of} u _L and u _{R is shown} in Figure 5d. This waveform is called a sawtooth pulse wave. In the actual circuit, the linearity of the scanning waveform is poor due to the non-linear characteristics of the transistor and the effect of the LC shunt of the choke coil.