Signal generators are devices that are primarily designed to test transmitters. Additionally, experts use them to measure the characteristics of analog converters. Testing of model transmitters takes place by simulating a signal. This is necessary to check the device for compliance with modern standards. Directly the signal to the device can be supplied in pure form or with distortion. Its speed through the channels can vary greatly.
What does the generator look like?
If we consider the usual model of a signal generator, then on the front panel you can see the screen. It is necessary in order to monitor fluctuations and conduct management. At the top of the screen is an editor that offers a variety of functions to choose from. Further below is a seven sensor, which shows the frequency of oscillations. Below it is a mode line. The amplitude or offset level of the signal can be adjusted using two buttons. For working with files there is a separate mini-panel. With its help, the test results can be saved or immediately opened.
In order for the user to be able to change the sampling rate, the generator has a special controller. By numerical values, you can quickly synchronize. The signal outputs are usually located at the bottom of the device under the screen. There is also a digging button to start the generator.
Homemade devices
Making a signal generator with your own hands is quite problematic due to the complexity of the device. The main element of equipment is considered to be a selector. It is designed in the model for a certain number of channels. There are usually two microcircuits in a device. To adjust the frequency, the generator needs a synthesizer. If we consider multichannel devices, then microcontrollers for them are suitable for the KN148 series. Converters are used only analog type.
Sine Wave Devices
The sine wave generator uses fairly simple chips. Amplifiers can only be used in the operational type. This is necessary for normal signal transmission from resistors to the board. Potentiometers are included in the system with a rating of at least 200 ohms. The pulse fill factor depends on the speed of the generation process.
For flexible device configuration, multi-channel units are installed. The frequency range is changed by the sinusoidal signal generator using the rotary knob. For testing receivers, it is only suitable for the modulating type. This suggests that the generator should have at least five channels.
Low Frequency Generator Circuit
The low-frequency signal generator (circuit shown below) includes analog resistors. Potentiometers should only be installed with a nominal value of 150 ohms. To change the magnitude of the pulse, modulators of the KK202 series are used. Generation in this case occurs through capacitors. There should be a jumper between the resistors in the circuit. The presence of two conclusions allows you to set the switch (low-frequency) in the signal generator.
The principle of operation of the sound model
By connecting an audio signal generator, the voltage is initially supplied to the selector. Next, alternating current passes through a bunch of transistors. After conversion to work, capacitors are turned on. Oscillations are reflected on the screen using a microcontroller. To adjust the limit frequency, special conclusions on the chip are needed.
The maximum output power in this case, the sound generator can reach 3 GHz, but the error should be minimal. To do this, a limiter is installed near the resistor. Phase noise is perceived by the system due to the connector. The phase modulation index depends solely on the current conversion rate.
Mixed Signal Design
The standard generator circuit of this type is distinguished by a multi-channel selector. There are more than five panel outputs. In this case, the maximum frequency can be set to 70 Hz. Capacitors in many models are available with capacities of not more than 20 pF. Resistors are most often turned on with a nominal value of 4 ohms. The installation time of the first mode is on average 2.5 s.
Due to the presence of a transmission limiter, the reverse power of the unit can reach 2 MHz. The frequency of the spectrum in this case can be adjusted using a modulator. There are separate outputs for output impedance. The absolute level error in the circuit is less than 2 dB. Converters in standard systems are available in the PP201 series.
Arbitrary Waveform Instrument
These devices are designed for small errors. Flexible sequence mode is provided in them. The standard selector circuit has six channels. The minimum frequency parameter is 70 Hz. Positive pulses by a generator of this type are perceived. Capacitors in the capacitance circuit have at least 20 pF. The output impedance of the device is maintained up to 5 ohms.
In terms of synchronization parameters, these signal generators are quite different. This is usually associated with the type of connector. As a result, the rise time ranges from 15 to 40 ns. There are two modes in total in the models (linear as well as logarithmic). With their help, the amplitude can be changed. The frequency error in this case is less than 3%.
Modifications to Complex Signals
To modify complex signals, specialists use only multi-channel selectors in the generators. Amplifiers they are equipped without fail. To change the operating modes, use the regulators. Thanks to the converter, the current becomes constant with a frequency below 60 Hz. Rise time on average should be no more than 40 ns. For this purpose, the minimum capacitance of the capacitor is 15 pF. The system resistance for the signal must be perceived in the region of 50 Ohms. The distortion at 40 kHz is usually 1%. Thus, generators can be used to test receivers.
Generators with built-in editors
The signal generators of this type are very easy to configure. Regulators in them are designed for four positions. Thus, the limit frequency level can be adjusted. If we talk about the installation time, then in many models it is 3 ms. This is achieved through microcontrollers. They connect to the board using jumpers. Bandwidth limiters in generators of this type are not installed. Converters according to the device scheme are located behind the selectors. Synthesizers are rarely used in models. The maximum output power of the device is at 2 MHz. The error in this case is allowed only 2%.
Digital Output Devices
Signal generators with digital outputs connectors are equipped with a series of KR300. Resistors, in turn, are turned on with a nominal value of at least 4 ohms. Thus, the internal resistance of the resistor is maintained large. Receivers with a power of not more than 15 V are capable of testing these devices. Connection to the converter is carried out only through jumpers.
Selectors in generators can be found three- and four-channel. The microcircuit in the standard circuit, as a rule, is used like KA345. Switches for measuring instruments use only rotary. Pulse modulation in the generators occurs rather quickly, and this is achieved due to the high transmission coefficient. Also note the low level of broadband noise at 10 dB.
High Speed Models
The high-frequency signal generator has high power. It is capable of withstanding internal resistance of 50 ohms on average. The bandwidth of such models is usually 2 GHz. Additionally, keep in mind that capacitors are used with a capacitance of at least 7 pF. Thus, the maximum current is maintained at around 3 A. The maximum distortion in the system can be 1%.
Amplifiers, as a rule, can only be found in operational generators in generators. Circuit limiters are installed at the beginning and also at the end. A connector for selecting the type of signal is present. Microcontrollers can be found most often in the PPK211 series. The selector is designed for at least six channels. Rotary controllers in such devices are available. The maximum limit frequency can be set at 90 Hz.
Operation of logic signal generators
This signal generator resistors has a nominal value of not more than 4 ohms. In this case, the internal resistance is kept quite high. To reduce the transmission speed of the signal, operational- type amplifiers are installed. The findings on the panel, as a rule, there are three. Connection to the transmit limiters takes place only through jumpers.
The switches in the devices are mounted rotary. Two modes can be selected. For phase modulation, signal generators of this type can be used. Their broadband noise parameter does not exceed 5 dB. The frequency deviation indicator, as a rule, is at around 16 MHz. The disadvantages include a long rise time, as well as a decline. This is due to the low bandwidth of the microcontroller.
Generator circuit with MX101 modulator
The standard generator circuit with such a modulator provides for the presence of a selector for five channels. This makes it possible to work in linear mode. The maximum amplitude at low load is maintained at 10 peaks. DC bias is quite rare. The output current parameter is at around 4 A. The maximum frequency error can reach 3%. The average rise time for generators with such modulators is 50 ns.
The waveform of the meander system is perceived. You can test receivers using this model with a power of no more than 5 V. The logarithmic sweep mode allows you to quite successfully work with various measuring instruments. The adjustment speed on the panel can be changed smoothly. Due to the high output resistance, the load from the converters is removed.