Sine wave

The LM12 is a power op amp capable of driving ±25V at ±10A while operating from ±30V supplies. The monolithic IC can deliver 80W of sine wave power into a 4 load with 0.01% distortion. Power bandwidth is 60 kHz. Further, a peak dissipation capability of 800W allows it to handle reactive loads such as transducers, actuators or small motors without derating.

This is a very simple 5 watt CW TX based upon a TTL logic chip. There is just one "tricky" component and this is Cx. This component should have an impedance of about 10 - 50 ohms at the frequency of interest. If you wish to reduce the transmitter power, increase the value of Cx. It is Cx which causes the square wave from the output transistor to approximate a sine waveform. The value of Cx is the price of simplicity in this TX.

Figure 2 shows a block diagram for this sine-wave generator. You can easily analyze the generator's behavior by writing state equations in the z domain. You can also write equations in the s domain. The location of the two poles on the right-hand side reveals the generator's oscillatory nature. The inverse Laplace transformation is simple and results in a sine-wave statement.

This circuit generates a good 1KHz sinewave adopting the inverted Wien bridge configuration (C1-R3 & C2-R4). It features a variable output, low distortion and low output impedance in order to obtain good overload capability. A small filament bulb ensures a stable long term output amplitude waveform. Useful to test the Precision Audio Millivoltmeter, Three-Level Audio Power Indicator and other audio circuits posted to this website.

This circuit generates a good 1KHz sinewave adopting the inverted Wien bridge configuration (C1-R3 & C2-R4). It features a variable output, low distortion and low output impedance in order to obtain good overload capability. A small filament bulb ensures a stable long term output amplitude waveform. Useful to test the Precision Audio Millivoltmeter, Three-Level Audio Power Indicator and other audio circuits posted to this website.

You can use a 68HC11 and a 12-bit serial DAC (Figure 1) to generate accurate sine waves without using floating-point arithmetic. Figure 2 shows a block diagram for this sine-wave generator. You can easily analyze the generator's behavior by writing state equations in the z domain. You can also write equations in the s domain. The location of the two poles on the right-hand side reveals the generator's oscillatory nature. The inverse Laplace transformation is simple and results in a sine-wave statement.

The multivibrator is a common circuit that consists of an amplifier with both positive and negative feedback (Figure 1a). When the output is positive, the positive input terminal equals ½V+, and the voltage at the negative input terminal changes toward V+. When this voltage exceeds ½V+, the output voltage rapidly changes to V–. The positive input terminal becomes ½V–, and the negative input terminal changes toward V–.

Figure 1 shows a technique for generating a high-quality sine wave from a square-wave source. Using textbook methodology, you can easily convert a square wave into a sine wave: Feed a square wave at the desired frequency into an appropriate four- to six-pole lowpass filter. The filter's output is a sine wave; the higher the order of the filter, the purer the sine wave. In practice, this conversion technique is difficult to implement, because such filters require several components and are difficult to adjust.

This Design Idea provides a simple, inexpensive, portable circuit as an alternative to a microcontroller to provide a wide-range source of low-distortion sine waves for audio-circuit design and debugging. Although sine waves from DDS (direct digital synthesis) offer greater stability and fewer harmonics and other spurious-frequency components, this more "retro" approach lets designers use Linear Technology Corp's LTSpice freeware and hone their circuit-simulation skills.

A simple technique provides phase compensation for the oscillator in Figure 1a. In this circuit, a tungsten lamp regulates the amplitude of a crystal bridge oscillator. This type of oscillator produces a very low-distortion output at a very stable frequency. The op amp must have a negligible phase shift at the operating frequency, which is the series resonance frequency of the crystal.

Electronic applications such as distortion and communications measurements require pure (distortionless) sine waves as input test signals. Distortion contained in test signals causes two problems. First, the test signal distortion content must be calibrated so it can be subtracted out of the measurement. Second, processing a distorted test signal usually creates unique harmonics which cause false readings because they can’t be calibrated out.

Using a current-feedback op amp, you can generate high-frequency sine waves with larger amplitude than conventional op-amp-based designs. The circuit in Fig 1 uses four passive components, connecting one capacitor to the compensation node (another op amp that has this pin available is the OP660).

Using current-feedback amplifiers to convert signals from sine waves to square waves for DSP confers advantages over the more common comparator approaches. Current-feedback amplifiers have wide bandwidths and relatively small and constant propagation delays. These small, constant delays help meet the setup-and-hold requirements of digital logic. Typically, current-feedback amplifiers have delays from 1.1 to 5 nsec.

The circuit of Figure 1 produces an accurate, variable-frequency sine wave for use as a general-purpose reference signal. It includes an eighth-order elliptic, switched-capacitor lowpass filter, IC3, which uses a 100-kHz square-wave clock signal that microcontroller IC2 generates. (Any other convenient square-wave source is also acceptable.) The microcontroller receives its clock signal from a 10-MHz oscillator module. A voltage supervisor, IC1, ensures correct operation in the event of a power failure.

A telephone DTMF IC produces, by design, two tones if you connect a single intersection of the IC's 4[x]4 keypad matrix (Fig 1). (Telephones commonly have 3Χ4 keypads but, unknown to many people, the applicable standard allows for a fourth row of four keys.) But, if you connect two key inputs at once, the IC produces a single-frequency, low-distortion sine wave.

One approach to generating sine waves is to filter a square wave. This leaves only the sine wave fundamental as the output. Since a square wave is easily amplitude stabilized by clipping, the sine wave output is also amplitude stabilized. A clipping oscillator eliminates the problems encountered with agc stabilized oscillators such as those using Wein bridges. Additionally, since there is no slow agc loop, the oscillator starts quickly and reaches final amplitude within a few cycles.

One of the troubleshooting tests required for telephone/data twisted-pair copper lines is the determination of the attenuation factor. The test uses frequencies of 300 to 4000 Hz to plot the attenuation performance. Because many central-distribution lines are in locations where power lines are unavailable, a battery-powered generator is desirable for the testing. The circuit in Figure 1 runs from 6 to 9V dry-cell batteries.

At the heart of many oscillators is a parallel-resonant LC tank circuit whose impedance is infinite at the resonant frequency of 1/2[pi]ΦLC Hz. Infinite impedance implies an absence of parallel damping resistance, so once an ideal tank circuit starts oscillating, it should continue indefinitely. An actual tank circuit, of course, has parasitic resistances that dissipate energy, causing the oscillations to die out.

Unlike a Wien-bridge oscillator, the phase-shift oscillator in Fig 1 starts up quickly. Also, the circuit does not require that you adjust several trimming resistors just to tune the oscillator to a given frequency. Experiments show that the circuit's total harmonic distortion (THD) measures approximately 0.5% or less.

Producing low-distortion sine waves, this oscillator operates over the range 16 to 22000 Hz. The circuit is based on two articles that have appeared earlier in Wireless World - Roger Rosens' "Phase -Shifting Oscillator", February 1982 pp. 38-41, and J. L. Linsley Hood's "Wien-Bridge Oscillator with low harmonic distortion" from May 1981 pp. 51-53. This design features the simplicity of the Rosens' circuit but avoids the use of a thermistor.