Non-sinusoidal wave generation circuits are similar in function to sinusoidal oscillation circuits, as they both produce signals with specific frequencies and amplitudes. Therefore, they also require attention to frequency stability, amplitude consistency, and waveform quality. Among these, frequency is the most critical parameter. As a result, non-sinusoidal oscillation circuits must be adjusted for frequency, amplitude, and waveform. Since the signal being measured is non-sinusoidal, an oscilloscope is typically used for observation, while a digital frequency meter can be employed to measure frequency. The adjustment and testing methods of non-sinusoidal circuits are generally similar to those of sine wave circuits, but there are some key differences that are worth noting.
1. Amplitude Adjustment: Non-sinusoidal circuits are commonly used to generate square or triangular waves. These circuits operate in a highly nonlinear region, producing only high and low-level outputs. Unlike sinusoidal circuits, the amplitude in non-sinusoidal circuits isn't determined by loop gain, but rather by the combination of current, voltage, and the supply voltage when the device enters a nonlinear state. To achieve stable and accurate amplitude, high-precision voltage regulators are often used to control the output levels. By changing the regulator's stable voltage, it's easy to adjust the desired output range. In non-sinusoidal circuits, the oscillation frequency is independent of the Zener diode's stable voltage, so adjusting the amplitude doesn't affect the frequency. For triangular waves, the amplitude can also be controlled by adjusting the upper and lower threshold voltages of the comparator. The amplitude is usually measured using an oscilloscope.
2. Waveform Adjustment: (1) When observing non-sinusoidal waveforms, an oscilloscope is essential. For square waves, the sharpness of the rising and falling edges is crucial. If the edges are not steep, it may indicate that the operational amplifier used as a comparator has a low conversion rate. This can be checked using a high-speed op-amp. The higher the oscillation frequency, the greater the required conversion rate of the op-amp. (2) For triangular or sawtooth waves, the linearity of the rising and falling edges is important. If the edges are rounded, it suggests poor linearity, which could be due to a lack of sharp transitions in the square wave. The steeper the square wave edges, the better the linearity of the triangular wave.
3. Frequency Adjustment: (1) Non-sinusoidal circuits typically do not include frequency selection components. The oscillation period is mainly determined by the energy change speed of the energy storage elements in the integrator circuit. Thus, the frequency can be adjusted by modifying the resistor or capacitor values in the integration circuit. Alternatively, the charging and discharging current of the current source can be changed to adjust the frequency without affecting the amplitude. (2) Frequency stability can be evaluated by measuring the variation in frequency over time. Consistent frequency output is essential for reliable performance in non-sinusoidal applications.
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