40 Common sense essentials for analog circuit engineers!
2024-04-24 14:22:03 20
1, electrical interface design, reflection attenuation is usually worse in the case of high frequency, this is because the loss of the transmission line reflection is related to the frequency, in this case, as far as possible to shorten the PCB line is extremely important.
2, the voltage regulator diode is a diode that stabilizes the working voltage of the circuit, due to the special internal structure characteristics, suitable for the working state of reverse breakdown, as long as the size of the limited current, this breakdown is non-destructive.
3, the PN junction has a very good mathematical model: the switch model → the diode was born → another PN junction, the transistor was born.
4. In high-frequency circuits, the influence of PN junction capacitance must be considered (forward bias is diffusion capacitance, reverse phase bias is barrier capacitance).
5, in the case of high density, because the receiving and receiving signals are next to each other, it is easy to cause crosstalk, which should comply with the 3W principle when wiring, that is, the center line spacing of the adjacent PCB line is greater than 3 times the width of the PCB line. In the card device, the position where the connector is connected, there should be many ground pins to provide a good RF loop.
6, bipolar tube is a current control device, through the base of the small current to control the larger collector current; MOS is a voltage control device that controls the source-drain on-resistance through the gate voltage.
7, the transistor is to work by the movement of carriers, npn tube emitter follower as an example, when the base plus voltage, the base and emission region of the pn to prevent multiple (base region for holes, emission region for electrons) of the diffusion movement, the pn junction will be induced by the emission region to the base area of the electrostatic field (that is, the built-in electric field).
8, Schottky diode (SBD) is suitable for high frequency switching circuit, forward voltage drop and reverse phase voltage drop are very low (0.2V), but the reverse breakdown voltage is low, leakage current is also large.
9, the jitter characteristics largely depend on the characteristics of the output chip, however, if the PCB is improperly routed, the power filter is not sufficient, and the clock reference source is too large, it will also increase the jitter component. The matching of signal lines has a direct effect on jitter. In particular, the chip contains frequency doubling function, and the phase noise itself is large.
10, the pole type selection refers to whether the BJT uses PNP or NPN tube, which should be considered at the same time when determining the form of the power supply. Some triode enclosures are connected to an electrode, which in the case of silicon tubes is often the collector. This factor should be taken into account when a pole needs to be grounded.
11, the field effect transistor and BJT have a big difference in the working process: the charge carrier in BJT is a small number of holes or knocked out of the "few sons", the charge in FET is the number of relatively several orders of magnitude more free electrons, "many sons".
12. Positive emitter bias and collector reverse bias are the prerequisites for BJT to work in the amplified working state. Three connection modes: common base, common emitter (at most, because current, voltage, power can be amplified), common collector. Three methods to distinguish the configuration: common emitter, base input, collector output; Common collector, base input, emitter output; Common-base, input by emitter, output by collector.
13, the main parameters of the transistor: current amplification factor β, electrode reverse current, (the maximum allowable current of the collector, the maximum allowable dissipation power of the collector, reverse breakdown voltage =3 important limit parameters to determine the BJT working in the safe area).
14, because the J-FET Rgs is very high, in use should first pay attention to electrostatic operation, otherwise it is easy to occur grid breakdown; In addition, the limit parameters should be carefully considered when designing the circuit and cannot be exceeded. When the J-FET is used as a variable resistor, it should be ensured that the device has a correct bias and cannot be allowed to enter the constant current region.
15, emitter bias circuit: used to eliminate the influence of temperature on the static operating point (double power supply is better).
16, three kinds of BJT amplifier circuit comparison: common emitter amplifier circuit, current and voltage can be amplified. Common collector amplifier circuit: only amplify the current, follow the voltage, the input R is large, the output R is small, used as the input stage, the output stage. Common base amplifier circuit: only amplify voltage, follow current, high frequency characteristics.
17, decoupling capacitor: the output signal capacitor is grounded, filter out the high-frequency clutter of the signal. Bypass capacitor: The input signal capacitor is grounded to filter out the high-frequency clutter of the signal. The AC signal is treated as a short circuit against both capacitors.
18, MOS-FET in use in addition to the correct selection of parameters and correct calculation, the most worthy of emphasis is still the problem of anti-static operation, in the circuit debugging, welding, installation process, must be strictly in accordance with the anti-static procedure operation.
19, the mainstream is from the emitter to the collector IC, bias is from the emitter to the base Ib. In contrast to the main circuit, the circuit that provides current to the base is the so-called bias circuit.
20, the field effect tube three aluminum electrodes: grid g, source s, drain d. Respectively corresponding to the triode base b, emitter e, collector c. < The source needs to emit something, so the corresponding emitter e, the English name of the gate is gate, the existence of the gate, and the role of the base is almost the same > where the P-type substrate is generally connected to the gate g.
21, the enhanced FET must rely on the gate source voltage Vgs to function (open voltage Vt), the depletion type FET does not need the gate source voltage, under the action of positive Vds, there is a large drain current flow to the source (if the negative Vgs, then there may be pinch, this voltage becomes pinch voltage Vp*** Important features *** : Can operate under positive and negative grid source voltage)
22, the n-channel MOS tube needs positive Vds (equivalent to the Vcc of the triode added to the collector) and positive Vt (equivalent to the Vbe of the triode base and emitter), while the P-channel MOS tube needs negative Vds and negative Vt.
23, VMOSFET has high input impedance, low drive current; Fast switching speed, good high-frequency characteristics; Negative current temperature coefficient, no heat vicious cycle, excellent advantages of heat stability.
24, operational amplifier application, generally use negative feedback current.
25, differential amplifier circuit: differential mode signal: the difference between the two input signals. Common-mode signal: Sum of two input signals divided by 2. Thus: Using the definition of differential mode and common mode to represent two input signals can obtain an important mathematical model: any input signal = common mode signal ± differential mode signal /2.
26, the differential amplifier circuit only amplifies the differential mode signal, and inhibits the common mode signal. Using this characteristic, the influence of external factors such as temperature on circuit performance can be well inhibited. Specific performance index: common mode rejection ratio Kcmr.
27, when the diode is converted from positive bias to reverse bias, there will be a large reverse recovery current from the cathode to the anode, and the reverse current rises first to the peak and then falls to zero.
28, in an ideal situation, if the two transistors of the push-pull circuit current, voltage wave is completely symmetrical, then the output current will have no even harmonic components, and the push-pull circuit by the known even harmonic function. In fact, because the characteristics of the two tubes are always different, the circuit can not be completely symmetrical, so the output current will also have even harmonic components, in order to reduce nonlinear distortion, because as far as possible to select the paired pipe.
29, in order to obtain a large output power, the voltage and current added to the power transistor are very large, and the transistor works in a large signal state. In this way, the safe operation of transistors becomes an important issue for power amplifiers, which generally do not exceed the limit parameters of the tube (Icm, BVceo, Pcm).
30, amplification circuit interference: 1, the power away from the amplifier circuit 2, input stage shielding 3, DC power supply voltage fluctuations (using a regulated power supply, input and output plus filter capacitor).
31, four configurations of negative feedback amplifier circuit: voltage series negative feedback (stable output voltage), voltage parallel negative feedback, current series negative feedback (stable output current), current parallel negative feedback.
32, voltage, current feedback determination method: output short-circuit method, set RL=0, if the feedback signal does not exist, voltage feedback, vice versa, it is current feedback.
33, the judgment method of series and parallel feedback: the summation method of the feedback signal and the input signal, if it is in voltage form, it is in series feedback, if it is in current form, it is in parallel feedback.
34, for the NPN circuit, for the common fire configuration, can be roughly understood as the VE as a "fixed" reference point, by controlling VB to control VBE (VBE=VB-VE), thereby controlling IB, and further control IC (from a higher potential into the C pole, you can also see the C pole as the funnel of water upward).
35, for digital circuits, VCC is the power supply voltage of the circuit,VDD is the working voltage of the chip (usually Vcc>Vdd), VSS is the ground point; In a field effect tube (or COMS device), VDD is the drain, VSS is the source, VDD and VSS refer to the component pins and do not indicate the supply voltage.
36, oscilloscope probe has a ground line and a signal line, the ground line is and oscilloscope input terminal housing through that one, generally clamp-like, signal line generally with a probe hook, connect then you connect the oscilloscope ground line to your equipment, the signal line terminal to your signal end, note that if the signal to be measured and the mains is not isolated, you can not directly measure.
37, there are two cases of insufficient driving capacity: first, the input resistance of the device is too small, the output waveform will be deformed, such as TTL level can not drive the relay; The second is that the input resistance of the device is large enough, but it cannot reach the power of the device, such as the low-power amplifier, which drives the high-power horn, the horn can sound, but the volume is very small, in fact, the output voltage is not large enough.
38, filter circuit: The use of reactance components of energy storage, can play a good filtering role. Both inductors (series, high power) and capacitors (parallel, low power) can act as flat waves.
39, switching regulated power supply and linear power supply: linear power supply has low efficiency, strong heat, but the output is stable. The switching power supply has high efficiency and ordinary heat, but the output ripple is large and requires flat wave.
40, the type of fault caused by the circuit: transistors, capacitors, resistors and other electronic components performance changes caused by the fault; The fault caused by the poor contact of the relevant line in the electronic circuit. The types of electronic circuit faults caused by external causes are: the technical personnel do not operate according to the instructions when using the electronic circuit; Maintenance technicians maintenance procedures are not standardized and scientific.
