Sine wave

Many applications require a sinusoidal reference voltage synchronized to the ac line voltage. You cannot derive such a reference voltage directly from the ac line because the waveform of the ac line is distorted because of nonlinear loads connected to the line and because the amplitude of the line signal varies. Hence, you cannot use a simple step-down transformer to derive the reference signal...

In this circuit the gain is provided by a FET type op-amp. I have used an LF351, which may be hard to obtain, but the TL071CN or TL081CN may be used and have a faster slewing rate than the LF351. The Maplin order codes are RA67X and RA70M respectively. The wien network is a parallel combination of resistor and capacitor, in series with a serial R-C network. Regenerative feedback is applied from the op-amp output, to the serail R-C input and continues...

We have already treated several kinds of relaxation oscillators in these units. The sine waves that your function generator creates are made from square waves, by wave-shaping circuits and filters, and are really not very good sine waves, though they do have most of their energy close to one frequency. If you need better sine waves, a linear oscillator will make them. A linear oscillator is very different from a relaxation oscillator...

The circuit requires only one power-switching device, and you can use an analog or a digital signal to drive the switching device. The circuit also requires only a few components: a diode, a switching transistor or a MOSFET, an inductor or a transformer, and a capacitor. Further, the design`s circuit losses are low, and the switching device experiences minimal stress during operation. Figure 1 shows the basic circuit, and Figure 2 illustrates waveforms within the circuit...

Rectangular pulse generators, even at high frequencies, are easy to design. However, the design becomes more difficult if you need a signal that contains a precise number of periods with a sinusoidal shape. Although it is easy to produce a good sine wave, the difficulty is producing a signal with a precise number of periods. The signal has to start and stop exactly at 0V. The scheme in Figure 1 can produce one to 15 periods of a 20-MHz sinusoidal wave...

This circuit was designed to provide a valuable test equipment tool for sound reinforcement systems like guitar amplifiers and the like. Used in conjunction with an ac voltmeter or other ac measurement tools, it can be of considerable help in setting and controlling levels through any amplifying chain...

A recent Design Idea described a method for designing simple, high-frequency LC oscillators with few passive components (Reference 1). However, for best results, practical hardware design of a stable oscillator requires more parts and greater complexity. Figure 1 shows a stable, 18-MHz oscillator with automatically leveled output amplitude control and an output buffer that delivers a sine wave with low harmonic content (Reference 2)...

To keep the gain constant, the circuit used an incandescent pilot light to provide AGC (automatic gain control). As is true for all incandescent bulbs, the pilot light has nonlinear resistance. When you turn on the circuit, the cold lamp`s resistance is low, resulting in high gain. As the gain increases, the resistance of the warming lamp increases. Thus, the lamp provides an AGC function...

This circuit produces an extremely low distortion sine wave, in spite of the non- linear devices used for amplitude limiting (D1 and D2). The reason is first that distortion (harmonics) is fed to the minus input of the opamp with far less loss than to the plus input, severely attenuating them. Second, this oscillator rides a delicate balance between negative and positive feedback...

A voltage-output DAC normally generates an output voltage that is a fraction of the input-reference voltage. In many designs, however, it is necessary to multiply the input voltage by a programmable gain, or, in other words, to create a variable-gain stage. You can easily implement a variable-gain stage using a low-cost voltage-output DAC (Figure 1)...

The circuit in Fig 1 generates a 50-Hz to 1-kHz sinusoidal waveform that exhibits lower than 60-dB THD. The input voltage controls the output frequency with the relationship 1 kHz/V. The output amplitude is invariant with frequency over the entire operating range. IC1 is a V/F converter with an input control range of 0 to 1V. You adjust R5 so that the output frequency equals 1 kHz with a 1V...

As a piece of test equipment, an audio oscillator has to be considered essential for anyone working in with hi-fi gear. Together with an audio millivoltmeter (as described in Project 16), and even better if you have access to an oscilloscope, you will be able to make proper measurements on everything from preamps, RIAA equalisation stages (for vinyl disks), tone controls, crossover networks, etc...