Signal generators are devices that are primarily designed to test transmitters. Additionally, experts use them to measure the characteristics of analog converters. Model transmitters are tested by simulating the 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 can vary greatly across channels.
What does the generator look like?
If we consider the usual model of the signal generator, then the screen can be seen on the front panel. It is necessary in order to monitor fluctuations and carry out control. At the top of the screen is an editor that offers a variety of functions to choose from. Further below is the sequencer, which shows the frequency of oscillation. Under it is the mode line. The amplitude or offset level of the signal can be adjusted using two buttons. There is a separate mini-panel for working with files. With it, test results can be saved either immediatelyopen.
In order for the user to be able to change the sample rate, the generator has a special regulator. By numerical values, synchronization can be done quite quickly. Signal outputs are usually located at the bottom of the device under the screen. There is also a 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 the equipment is considered to be the selector. It is calculated in the model for a certain number of channels. There are usually two microcircuits in the device. To adjust the frequency, the generator needs a synthesizer. If we consider multi-channel devices, then microcontrollers for them are suitable for the KH148 series. Converters are used only analog type.
Sine signal devices
The chip's sine wave generator uses fairly simple ones. In this case, amplifiers can only be used of the operational type. This is necessary for the normal signal transmission from the resistors to the board. Potentiometers are included in the system with a nominal value of at least 200 ohms. The pulse duty cycle depends on the speed of the generation process.
For flexible configuration of the device, blocks are installed multi-channel. The frequency range of the sinusoidal signal generator changes with a rotary control. For testing receivers, it is suitable only 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 set to 150 ohms. To change the magnitude of the pulse, modulators of the KK202 series are used. Generation in this case occurs through capacitors. There must be a jumper between the resistors in the circuit. The presence of two leads allows you to install a (low-frequency) switch in the signal generator.
How the beep model works
Connecting the audio frequency signal generator, the voltage is initially applied to the selector. Next, the alternating current passes through a bunch of transistors. After conversion to work, capacitors are turned on. Vibrations are reflected on the screen using a microcontroller. To adjust the limit frequency, special pins are needed on the microcircuit.
The maximum output power in this case, the audio signal 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 at the expense of the connector. The phase modulation index depends solely on the current conversion speed.
Mixed signal device diagram
The standard oscillator circuit of this type features a multi-channel selector. At the same time, there are more than five outputs on the panel. In this case, the maximum frequency limit can be set to 70 Hz. Capacitors in many models are available with a capacity of not more than 20pF. Resistors are most often included 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 bandwidth 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 the 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 Device
These devices are designed for a small error. They have a flexible sequencing mode. The standard selector circuit assumes six channels. The minimum frequency setting is 70 Hz. Positive impulses are perceived by the generator of this type. Capacitors in the circuit have a capacitance of at least 20 pF. The output resistance of the device is maintained up to 5 ohms.
These signal generators are quite different in timing parameters. It is connected, as a rule, with the type of connector. As a result, the rise time ranges from 15 to 40 ns. In total, there are two modes 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 of complex signals
To modify complex signals, specialists use only multi-channel selectors in generators. They are equipped with amplifiers without fail. Regulators are used to change operating modes. Thanks to the converter, the current becomes constant withfrequency below 60 Hz. The rise time should be no more than 40 ns on average. For this purpose, the minimum capacitance of the capacitor is 15 pF. The resistance of the system for the signal must be perceived in the region of 50 ohms. Distortion at 40 kHz is typically 1%. Thus, generators can be used to test receivers.
Generators with built-in editors
The signal generators of this type are very easy to set up. Regulators in them are designed for four positions. Thus, the cutoff frequency level can be adjusted. If we talk about the setup time, then it is 3 ms in many models. This is achieved through microcontrollers. They are connected to the board with jumpers. Transmission limiters are not installed in generators of this type. According to the device diagram, the converters are located behind the selectors. Synthesizers are rarely used in models. The maximum output power of the device is at the level of 2 MHz. The error in this case is allowed only 2%.
Devices with digital outputs
Signal generators with digital outputs are equipped with connectors for the KP300 series. Resistors, in turn, are included with a nominal value of at least 4 ohms. Thus, the internal resistance of the resistor is maintained large. Receivers with a power of no 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. Chip in standardchains are usually used type KA345. Switches for measuring instruments use only rotary ones. Pulse modulation in generators occurs quite quickly, and this is achieved due to the high transmission coefficient. You should also consider the low level of broadband noise at 10 dB.
High clocked models
The high clock frequency signal generator has high power. Internal resistance it is able to withstand an average of 50 ohms. The bandwidth of such models is usually 2 GHz. Additionally, it should be borne in mind that capacitors are used with a capacity of at least 7 pF. Thus, the maximum current is maintained at around 3 A. Distortion in the system can be maximum 1%.
Amplifiers, as a rule, can only be found in generators of the operational type. Limiters in the circuit are set at the beginning, as well as at the end. A connector for selecting the type of signals is present. Microcontrollers can be found most often in the RRK211 series. The selector is designed for at least six channels. Rotary regulators in such devices are available. The maximum frequency limit can be set to 90 Hz.
Operation of logic signal generators
This signal generator resistors have a nominal value of not more than 4 ohms. At the same time, the internal resistance is kept quite high. To reduce the signal transmission rate, operational-type amplifiers are installed. As a rule, there are three conclusions on the panel. Connection with limiterstransmission occurs only through jumpers.
The switches in the devices are installed rotary. Two modes can be selected. For phase modulation, signal generators of the specified 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. Disadvantages include long rise and fall times. This is due to the low bandwidth of the microcontroller.
Originator circuit with MX101 modulator
A standard oscillator circuit with such a modulator provides for a selector for five channels. This makes it possible to work in a linear mode. The maximum amplitude at low load is maintained at 10 peaks. DC bias occurs quite rarely. The output current parameter is at around 4 A. The maximum frequency error can reach up to 3%. The average rise time for oscillators with these modulators is 50 ns.
Meander waveform is accepted by the system. You can test receivers using this model with a power of no more than 5 V. The logarithmic sweep mode allows you to work quite successfully with various measuring instruments. The tuning speed on the panel can be changed smoothly. Due to the high output impedance, the load from the converters is removed.
