Sine wave oscillator design and production, SINE WAVE OSCILLATOR DESIGN
Keywords: design and production of sinusoidal oscillator
Sine wave oscillator design and production
When the debugging of the audio amplifier, it is often required to be low-missing sinusoidal signal generator. There is a sine wave generator that is necessary, this article design and production can achieve this.
The sine wave oscillation circuit has a variety of, but commonly used is Wenth bridge oscillator, Figure 1 is a schematic diagram of the principle. The in-phase input of the op amp is positively feedback, and the resonant frequency determines the oscillator frequency f = L / 2πrc; in the amplifier inverted input, the resistance is negative feedback, R1 / R2 The ratio determines the oscillation waveform. When the R equal and C is equal in the positive feedback loop, the gain of the amplifier is equal to 3, the circuit starts, that is, R1 = 2R2. If R1<2R2, the circuit will stop; and R1>2R2, the top of the output waveform will be compressed into flat top. Therefore, there is a stable gain stability for the Wen's bridge oscillator. Commonly used stability is to use bulbs instead of resistance R2, or with negative temperature coefficient thermistor replacement R1. The principle of using the bulb is that if the current increases, the electrical resistance of the filament becomes large, and the negative feedback amount is reduced to reduce the gain. The principle of thermistor using a negative temperature coefficient is: the current increases, the resistance of the thermistor becomes small, and the result is also reduced gain to increase the negative refueling.
The design goal of this sine wave oscillator is: frequency range 20Hz ~ 20kHz, which is continuously adjustable in three bands. The whole machine circuit is shown in Figure 2. Used as an oscillator, the oscillation frequency is preferably more reliable in one tenth of the op amp frequency parameters. The frequency-band width of 15 MHz is used here, which is available for eight feet gold, but the author uses a double-column-in-line-placed integrated block.
In order to gain stability, 12V, 60mA small electroless beads, the resistance value of 12 ÷ 0.06 = 200Ω. According to the aforementioned catenor principle, R1 = 2r2 = 400Ω, taking into account the adjustment margin, R1 selects 1 kΩ fine-tuning resistance.
The oscillation frequency is coarse-conditioned by two-knife five-bit band switch (only three digits), respectively, and the frequency elimination is adjusted with the coaxial dual-connected potentiometer W1. The output amplitude of the oscillator is adjusted by the potentiometer W2, and then divided by the buffer to isolate the oscillation circuit and the measured circuit, so that the oscillation frequency is not affected by the input impedance of the measured circuit. The buffer is set to follow the follower with single shipping LF356.
The power supply supplies + 15V and -15V voltage supply from three-end adjustable regulatory compression integrated circuits 7815 and 7915, respectively.
Circuit component selection: oscillator capacitor should use film capacitance, with withstand voltage is 50V, and the capacity needs to be selected with digital capacitance. The smaller the error, the better. The frequency adjustment potentiometer W1 uses a metal casing seal dual-link, and the resistance change characteristics are linear (Model suffix "x"). Slow rotating the potentiometer shaft when purchasing, measuring the resistance of each position, requires the difference between the two connectors to be substantially the same. If the resistance of a certain location is large, it cannot be used.
After the circuit assembly is installed, it will be commissioned and scaled. Firstly, the waveform of the generator-operator-out end is measured. At each of the gear and W1, there should be a sine wave output of a complete waveform, and there is no stop-changing point or a flat top waveform, otherwise the R1 should be fine. In the case where there is no oscilloscope, the actuator output can be connected to a 5V (or 10V) AC voltage meter, and the adjustment R1 has simulinated the voltage table, and then fine-tuned a point R1 in the reverse direction, so that the voltage meter has an indication in the range of the voltmeter. Otherwise, the above steps should be repeated. Be
The scale method still uses frequency gauges and equal circular weapons, blocking the frequency and grid comparison table, plotting the frequency dial. The measured frequency range of this generator is shown in the schedule (only the intermediate three gear when actually produced), the maximum output voltage 5VRMS, the distortion rate is 0.25% to 0.5% in the range of 1VRMs, the output 1VRMS, 20 Hz to 20 kHz. If you need to expand the frequency range, you can add a capacitor yourself. The maximum oscillation frequency of this circuit is up to 400 kHz, but the distortion rate has reached 3%.
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