Wednesday, December 29, 2010

【Weak current College】】 signal source basics.

<br> 1. understand the function generator signal generator General divided function generator and arbitrary waveform generators, function generator is designed also distinguish between analog and digital synthesis type. We all know that digital synthesis-function signal source both frequency and amplitude and signal to .noise ratio (S / N) superior simulation, the phase-locked loop (PLL) design so that the output signal is not only accurate frequency, and phase jitter (phase Jitter) and frequency shift are able to achieve rather stable state, but after .all, is a digital signal, digital and analog circuit interference between, always difficult to effectively overcome, resulting in small signal output than analogue of function generator. Referring to the analogue function signal source, chart as follows: this is a universal signal generator for .analogue function structure, triangle wave generation circuit is based on the diode by sine wave shaping circuit produces a sine wave, and through the comparator compares the resulting square wave. The triangle wave is generated, the formula is as follows: in other words, if .a constant current source for capacitor charging, you can have a positive slope of the ramp. Similarly, the right to constant current source will be stored in the capacitor discharge of charge on that produce negative slope of the ramp, the circuit structure is as follows .: when the I1 = I2, to produce a symmetrical triangle waves, if I1 I2>>, which produce negative slope of Sawtooth wave, similarly I1 I2 <<that have a positive slope sawtooth wave. Then, as shown in .Figure 2, can be switched SW1 choice so that multiple charging speed is changed, the change in the signal's frequency is the frequency of signal source Panel of select switch. The same synchronization changes I1 and I2, or you can change the frequency, this is .the signal source, adjust the frequency of a potentiometer, just need simply be originally voltage signals into electrical current. The duty to adjust the design of any of the following two ways: 1, frequency (period), pulse width change, its methods are .as follows: change level, ie change square wave generation circuit comparator reference amplitude, pulse width can be reached to change the frequency of the same features, but its major drawback is the duty of General cannot be transferred to below 20%, resulting in sampling .circuit experiments on transient signals in the acquisition of signal changes, if you want to add this signal for analog to digital (A / D) conversion, the resulting digital signal changes and what to do. But undeniable use better. 2. duty cycle frequency .variable, followed by change, its methods are as follows: place the square wave generation circuit comparator reference margins be fixed (positive and negative can be using circuit switching), change the slope, to charge and discharge. In this way by design user's response .was "difficult to tune," this is a big drawback, but it can produce 10% duty ratio below is a sampling of the necessary conditions. The above two duty ratio adjustment circuit design ideas, has advantages and disadvantages, of course, the associated .also affects whether you can produce a "decent" sawtooth wave. The next PA (power amplifier) design. First is the use of operational amplifier (OP), and then make use of push-pull (push-pull) amplifier (note the .crossover distortion Cross-distortion prevention) will signal to the attenuation of the Internet, this section applies to signal source output signal indicator contains the SNR, square-wave signal rise time and frequency response, signal source, of course, is a sine wave signal .to noise ratio high, square wave rise time fast, triangular wave linearity better, while v-frequency characteristics are slightly better (ie, the frequency increases, the signal does not decay or cannot be reduced too big), this part of the circuit is .more complex, especially in the high-frequency capacitance for when in addition to the use of frequency compensation, also involves the PC Board wiring methods, it's all too easy, very easy to cause oscillation, want to designed this part of the circuit, in .addition to the original simulation theory base needed to have actual experience, "Try Error" patience is indispensable. PA signal out, after the π-resistive attenuator networks, namely the attenuation of 10 times (20dB) or 100 times (40dB), then .a basic function waveform generator that has been completed. (Note: selection of π-attenuation networks instead of divider circuit is to maintain a certain output impedance). A strong function waveform generator, and sweep, VCG, TTL, TRIG, GATE and frequency .meter, its design in this way: 1. Sweep: generally divided into linear (Lin) and the log (Log) sweep; 2. VCG: ie General FM, enter an audio signal, and signal sources its own signal generation frequency modulation; .these two design styles, 1 to produce a sawtooth wave logarithmic wave signal, and 2 input signal passes through multiplier (Multiplexer) select, and then the voltage on power conversion circuits, synchronization to add to Photo 2 of I1 and I2; 3. TTL .synchronization output: square wave with transistor circuit to 0 (Low), 5V (High) TTL signal. But note that TTL signal must longer buffered Mun (buffer) to output in order to increase the fan-out (Fan Out), sometimes also .in parallel to several buffer. But as long as the TTL INV NOT Gate can add; 4. TRIG functions: similar to the One Shot function, enter a TTL signals, you can let the signal source produces a cycle of signal output, design patterns .are no signal input, the figure of the SWI grounding; 5. Gate function: enter a TTL signals, signal source in input for Hi, generate wave output until the input is LOW, the figure 2 SWI grounding and turn off the signal source output .; 6. Frequency meter: in addition to market and easy dial displays, regardless of whether they are LED digital tube or LCD display frequency, the frequency meter circuits are overlapping, and block diagram below: <br> 2. arbitrary waveform generator, Simulink's .best instruments arbitrary waveform generator is a signal source, it has a signalThe characteristics of the source of all. Our tradition that signal source key to be logging circuits provide needed known signal (various waveforms), and then use other instruments measure the parameters of interest .. Visible signal source in an experiment and test processing, and does not measure any parameter is based on the consumer's request, the simulation of test signal to be logging circuit to test needs. There are a variety of sources, including sine wave signal source, .function generators, pulse generators, scan generator, arbitrary waveform generator, synthesized signal source, etc. In general the arbitrary waveform generator, is a special kind of signal source, integrated with other signal source waveform generation capabilities, and thus suitable for the needs of .various simulation experiment. First, the function function, simulation based laboratory designers environment function signal source is the most widely used general signal source, it provides a sine wave, sawtooth, square, pulse train, waveform, and some also have a modem and scanning .capabilities, we all know, in our basic experiment (such as University electronic laboratory, scientific research institutions research laboratory, plant development labs, etc), we designed a circuit, it is necessary to verify the reliability and stability, it is necessary to impose .the ideal profile to tell the true from the false. If we can use the source DC compensation function on solid state circuit control DC bias voltage level; we can on a suspect digital circuit, using the square-wave output signal sources as digital circuit for .clock, at the same time, use the square wave and DC compensation effective logic level analog output, observation of the health of the circuit, and confirmed the bug. In general use arbitrary waveform generator this basic function, capable of simulating your basic laboratory must .signal. Second, arbitrary waveforms, simulation of more complex signal requirements as we all know, in our actual electronic environment design of the circuit in the run, due to various disturbances and response exists, there is often the actual circuit signals defects and transient signals ., such as a pulse, peak, damped transient, frequency of mutations, etc. (see Figure 1, Figure 2), these conditions, such as the beginning of the design is not taken into consideration, there would have disastrous consequences. For example .in Figure 1 has a Department, if spikes to a shock poor circuit, may cause the device to "burn out". Confirm that the circuit on a position-sensitive degree, we can avoid unnecessary losses, the requirements in the aerospace, military, .railway and some cases are more complex and important areas of particular importance. Due to the arbitrary waveform generator special features to enhance arbitrary waveform generation capabilities, it often rely on computer communication output waveform data. In the computer transmission, through dedicated waveform editing software generated .waveform, and help to expand the instrument's ability to further simulation experiment. At the same time, due to editing an arbitrary waveform sometimes need to spend considerable time and effort, and each time you edit waveforms may vary so some arbitrary waveform generator, built- .in a number of non-volatile memory, random access editing waveform comparison, conducive to reference; or through random interface communications transmitted to the computer for further analysis and processing. Third, download, transfer, real-time simulation in the military, aerospace, .transportation, manufacturing, and other areas, some circuit running environment it is difficult to estimate, in experimental design is complete, in the real environment is also a need for further experimentation, some experiments of high cost or risk is large (such as the train .tracks transform when high-speed experiment, when the propeller aircraft on the run, etc.), it is impossible to judge the design for experimental products (such as high-speed trains, planes) feasibility and stability; we can use some arbitrary waveform .generator waveforms download function, in some trouble costs or risk large experiment, through digital oscilloscope and other instruments to waveform record, and then in real time through the computer interface to the signal source, direct download to the design of the circuit, further experimental validation .. In summary, arbitrary waveform generator is an electronics engineer signal simulation experiment of the best tools. We purchase is in addition to the interest in traditional signal source defects - - frequency accuracy, frequency stability, increase accuracy, signal distortion, should be concerned about .its editorial and waveform survival and download capabilities, while also noting that the number of output channels, so that synchronization can compare the two signal phase shift, further reach simulation State. <br> Figure 1 a sharp pulse of the digital signal <br> .Figure 2 a square-wave frequency of mutations.

No comments:

Post a Comment