Signal generators: scheme, principle of operation, device and reviews
Signal generators are used in the design of electronic devices. They are used to test radio transmitters, receivers, audio amplifiers. The generator allows you to create a signal with the required amplitude, frequency and period. This simulates the signals that will be sent to the device during operation. The device is indispensable, as it allows you to test the operation of any device in all modes.
What do generators look like?
Standard generators of a sinusoidal signal are presented in the form of a small box, on the front panel there is a screen. It is used to control vibrations and adjustments. At the top of the screen there is a text box - this is a kind of menu, in which there are different functions. Control can be done with buttons and variable resistors.On the screen indicates all the information needed when working.
The amplitude and offset of the signal are adjusted using the buttons. The latest models of devices are equipped with outputs, through which you can record all the results on a flash drive. To change the sampling frequency in the generators of a sinusoidal signal, special regulators are used. Thanks to them, the user can synchronize very quickly. Usually at the bottom, below the screen, is the power button, and next to it are the generator outputs.
You can make a signal generator with your own hands from improvised means. The main part of any generator is a selector (English select is a choice). In any design it is designed for multiple channels. In standard designs used no more than two chips. This for the implementation of the simplest devices is enough. Ideal for the manufacture of chip generators from the KH148 series. As for the converters, they are used only analog.
In some cases it is allowed to use a personal computer as a signal generator.The hands can make a small adapter - it is installed at the output of the sound card. The signal is removed from the output and is used to test the equipment. A program is installed on the PC that will control the sound card. The disadvantage of this design is too narrow a range of frequencies, so it cannot be used when testing some devices.
Sine Wave Generators
Sine is the most common waveform generator. It is necessary for testing most of the equipment. The design uses the most simple chips. They produce a signal that is converted by an operational amplifier. To adjust the signals, it is necessary to include variable or fixed resistors in the circuit. It depends on the type of resistance used, stepwise or smoothly adjustment will be carried out.
Sine-wave signal generators are widely used for tuning not only radio equipment, but also high-frequency equipment — inverters, power supplies, frequency converters for asynchronous motors, etc.This technique allows the conversion of the original sine of a household network (frequency 50 Hz). Moreover, the frequency increases tenfold - up to 100 MHz. This is necessary for normal operation of the pulse transformer.
Low frequency generators
Such designs are used to configure and test audio equipment. If you pay attention to the scheme of the simplest low-frequency signal generator, you can see that variable resistors are installed in it - they are used to adjust the shape and size of the signal. To make a change in the magnitude of the pulse, you can use the KK202 series modulator. The signal in this case must be generated via capacitors.
A low-frequency signal generator is used to tune any audio equipment such as players, audio amplifiers, etc. You can use a personal computer as such a generator (even an old laptop will do). This is a budget option that does not require large expenditures if an old computer is available. It is enough to install the latest version of the drivers, the program for working with a sound card and make an adapter for connecting to the equipment.
How sound generators work
But if we are talking about standard designs made on chips, then the voltage is applied to the selector. The signal is generated by one or several microcircuits.
Typically, the circuit consists of a single chip, which sets the frequency:
- A quartz resonator tuned to a specific frequency is connected to one input.
- A variable resistor is connected to the other input of the microcircuit (the nominal value is chosen empirically). With it, you can adjust the fluctuations.
- The chip allows you to increase or decrease the frequency produced by quartz, to any value.
- The microcircuit is flashed (if necessary) so that when the knob is turned, the frequency changes.
The maximum frequency that the device can generate depends on the chip used and the quartz. The value of 3 GHz is the highest for most designs. To reduce the error limiters are installed.
Mixed Signal Generators
The standard design has a multi-channel selector. On the front panel of the generator, generating a signal with a minimum frequency of 70 Hz, there are at least five outputs.The ratings used in the design of resistance - 4 ohms, capacitors - 20 pF. The generator goes into operation for 2.5 seconds.
The reverse frequency of the device can be adjusted in a wider range - up to 2000 kHz. In this case, the frequency is controlled by the modulation device. The instrument error (absolute) is no more than 2 dB. For standard signal generators, the PP201 series is used.
Arbitrary pulse generator
These devices have one feature - they have a very small error. The design also provides for fine adjustment of the output signal - for this, a six-channel selector is used. The minimum frequency produced by the generator is 70 Hz. Positive impulses are perceived by such generators. The circuit uses capacitors, capacitance not less than 20 pF. The output resistance of the device is no more than 5 ohms.
All arbitrary waveform generators differ in synchronization parameters. This happens because of the type of connector installed. For this reason, the increase in the signal can occur over a time of 15-40 ns.Depending on the generator model, there may be two types of modes in it - logarithmic and linear. With the help of appropriate switches, they can be changed, which will entail an amplitude correction. The total error of frequency is not more than 3%.
Complex signal generators
DDS-signal generator can be called a design that allows you to receive pulses of complex shape. In such constructions only multichannel types of selectors are used. The signal produced is necessarily amplified, and regulators are used to change the operating mode.
The total rise time of the signal is no more than 40 ns. To reduce the time used capacitors with a capacity of not more than 15 pF. The output impedance of the device is about 50 ohms (standard value). When operating at 40 kHz, the distortion does not exceed 1%. Such generator designs are widely used for testing radio receivers.
All low and high frequency signal generators are very easy to set up. They have several four-position knobs that allow you to adjust the value of the maximum frequency.The transition time to the steady state in most models is no more than 3 ms. Such a short time can be achieved through the use of microcontrollers.
Microcontrollers are mounted on the main board, in some designs they are removable - in just one movement you can install a new element. In designs with a built-in editor no limiters are installed. After the selectors for the scheme are converters. Sometimes in the schemes can be found synthesizers. The maximum frequency of the generated signal can be 2000 kHz, the total error is not more than 2%.
Digital Signal Generators
You looked at how the sound generator works to test bass amplifiers. But nowadays, the widespread popularity of digital technology - a variety of controllers, gauges that need more fine-tuning. Connectors used in such generators - КР300. The design resistors have a resistance of not less than 4 ohms. Due to this, it is possible to maintain a large internal resistance of the whole structure.
In the digital signal generators, three- and four-channel types of selectors are used, built on a KA345 chip.In designs, pulse modulation occurs, since the transmission coefficient is very high. Broadband noise is extremely low - no more than 10 dB. These designs allow you to generate rectangular signals. They are necessary for fine-tuning the operation of digital circuits.
High frequency designs
The internal resistance of the high-frequency signal generator is about 50 ohms. In this case, the device is able to give more power. For high frequency designs, the bandwidth is about 2 GHz. The circuit uses fixed capacitors with a capacity of more than 7 pF. This allows you to maintain the maximum current in the circuit up to 3 A. Distortion at the level of 1%.
In high-frequency generators, only operational amplifiers are used. Signal limiters are mounted at the beginning and end of the circuit. For work, microcontrollers from the PPK211 series and a six-channel selector are used. Using the knobs, you can set the output frequency - the minimum value of 90 Hz.
The design uses fixed resistors, the nominal value of which does not exceed 4 ohms. Due to this, a very high internal resistance is maintained. To reduce the speed at which the signal is transmitted, an operational amplifier is used.On the front panel in standard designs there are three outputs that are connected to the bandwidth limiter by jumpers.
The signal generator circuit uses switches. The most commonly used is the rotary type, which allows you to choose one of two modes. These types of oscillators can be used for phase modulation. The maximum level of noise in most structures does not exceed 5 dB. Deviation (care) of the frequency of not more than 16 kHz. Among the disadvantages of structures of this type, we can distinguish a large signal rise time, since the throughput of the microcontroller is very low.
Reviews of simple designs that are sold in stores, a variety. Some buyers note that the steps are too noticeable in the generators (although the curve should be smooth). Because of this, it is not possible to properly configure audio equipment. Other buyers note that the generators do not work in one or several ranges. If you need quality and reliability, then get a multifunctional generator. It will allow you to configure any equipment - from audio amplifiers to radio transmitters of cell phones.Cheap designers, which are enough in stores, allow only a rough adjustment of the equipment. Such a signal generator supports the frequency well, but the shape of the curve leaves much to be desired.