Op-amps are almost perfect amplifiers. As long as you remember some important details, they will look perfect。
In section 1, i will briefly describe how the operator amplifier used as a server amplifier can be applied to the size signal by comparing the small signal with the decay signal from the amplifier output. I say the amplifier works to make feedback equal to input. When negative feedback is not configured, the algorithm amplifier has very high voltage gain - possibly 100 k-v/v or 1 m-v/v - and is therefore almost unlimited. If the gain is unlimited, the server (figure 1) will equal the negative input end with the positive input end. The differential input level will be scaled up by a differential to input voltage (which we have just defined as zero) and multiplied by an unlimited gain, which will produce an unknown output because it is not defined mathematically。
Figure 1. This is a simple single power circuit with an ac coupling at both input and output points. Electricity gain
Look again at figure 1, when you provide a small signal to the same input (r13-c6 node) of the compute amplifier, magnify it by a very large number, and then send the output (in +c7) to the reverse input (r9-r10 node) of the compute amplifier, the server action disappears, but not zero. The near-zero is directly related to the extent to which the greater v/v is close to unlimited voltage gains. The level of distortion is also relevant. Of course, the perfect amplifiers don't fall apart。
I'm going to look into this at the end of this paper and i'm going to give you a mathematical analysis. Nevertheless, i hope that this simplified and intuitive approach will create a framework of understanding。
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Any operation amplifier made of a bipolar transistor, jfet, mosfet, or even a vacuum tube, is less than desirable. The main disadvantage of the input level is the input deflection of the voltage and the input bias of the current. In figure 2, this is a simplified version of the previous amplifier circuit. To simplify input bias circuits, it is powered by a bipolar power source. For the sake of clarity, output trading capacitor and general bypass capacitor were omitted。
Figure 2. To understand the true operation amplifier, a perfect operation amplifier may be considered, with very little input disordered voltage at the differential input end。
In order to symbolically describe what input of a dysfunctional voltage is like, we can imagine a microbattery associated with input of a perfect operation amplifier, as shown in figure 2. Their end voltage may be in the range of a few milliwatts. Polarity can be either reversed, as shown in the figure, depending on the specifics of the input structure of the compute amplifier。
For amplifiers used in conjunction with communication signals, such as audio pre-amplifiers, sensor rotors, vibration sensors and rfs, the deviation is usually negligible. For amplifiers used in conjunction with direct-flow signals, such as thermoelectric dolls, photovoltaic detectors, electrostatometers and electrochemical cells, adjust and eliminate any disordered voltage using low-discompression computing amplifiers or adding circuits。
Figure 3。
In order to symbolically show what type of input bias is, we can add a small current source to the input end of the compute amplifier, as shown in figure 3. The currents range from millimetres to microan. Their polarity may be as shown or otherwise, depending on the input structure of the operator amplifier。
The offset current will pass through the resistance of the flow-calculating amplifier input end (thus r6 for the same input and r4/r5 for the reverse input). If these do not match, preference for current flow and subsequent i-r voltage will effectively generate additional deflection voltage. As noted above, it may be necessary to render it ineffective。
Bandwidth or frequency response
After resolving the main issues surrounding the input of the compute amplifiers, we now turn our attention to bandwidth specifications. The bandwidth of an operating amplifier is usually expressed as an increase (i. E., no feedback added) for its open-ring voltage until the gain is reduced to a frequency of 1 or 0. 0 db. As a result of the low access properties of the internal circuits, the gain decreases as the frequency increases. Usually, internal capacitor and associated driver resistance (i. E. Low-throughput component) create a dominant polar point, which rolls down from frequency. See, for example, a part of the lf444 data manual for the texan instrument (ti) four channel operators, as shown in table 1. I drew a blue frame around the spec, which is a part of the typical open ring gain. Gain bandwidth (gbw) is shown as 1 mhz (typical value)。
Table 1. Lf444 a partial increase bandwidth. (photo by texas industries)
Figure 4. This figure shows the relationship between open-ring gain and frequency in part of lf44. (photo by texas industries)
Now, with reference to figure 4 in the same data table, we see the relationship between the gain and the frequency, from very low frequency (possibly straight flow) to 10 hz, and the relationship between the gain and the frequency is 100 db. It then rolls down in a straight line and reaches 0 db point around 1 mhz. Thus, the information shown in the typical chart is consistent with the data in the table. Remember that the x-axis (frequency) and y-axis (voltage gain) are logarithmic, so each tic on the x-axis is ten times the frequency range (10, 100, 1 khz, etc.) and each tic on the y-axis is 20 db (20, 40, 60, etc.). A logarithmic logarithmic scale makes it easier for us to perform some of the assessments: you can add or subtract gains in fractions instead of v/v multiplied by gains。
Figure 5. In this example, the gain configuration of the operator amplifier is –r1/r2 or –10 v/v. A minus sign is the inverse amplifier in which vout is measured relative to vin。
Note that simply because the bandwidth of the operation amplifier is extended to 1 mhz does not mean that you can use the operation amplifier to zoom the signal to 1 mhz. Well, you can, but you won't be satisfied with the results. In order to understand the reasons, we will study in depth the operation of the amplifiers and consider the comparison of closed and open responses。
This is a very simple circuit if you want to use the audio pre-memplifier circuit with an operation amplifier of 10 v/v (equivalent to +20 db). Figure 5, select r1 = 10. 0 k and r2 = 1. 00 k。
Figure 6. The blue line represents closed-ring gain in the operation of amplifier circuits。
To see what that circuit is going to do, we can superimpose it on an open-loop map. As shown in figure 6, i added the blue line。
From v to v, we get 20 db gains on 100 khz. The closed circle gain then tracks the open circle gain to 1 mhz, at which point the gain becomes 0 db (or gain 1 or 1). It looks good enough for the audio, right? No. In fact, this is highly undesirable. The increase in khz is only 20 db (mathematical difference between opening and closed circle gain), while the gain in 10 hz is 80 db. That means you're going to fall apart。
Figure 7. Feedback is not used in the open ring system。
We will revisit the starting point of the server amplifier design to gain a better understanding. We do not use the algorithm amplifier symbols and specific resistors, as in figure 1 and figure 6, but rather draw blocks and add the necessary values to indicate the points of gain, decay and signal add-on (similar to the differential input structure of the amplifier). Therefore, the open-ring amplifier and associated gain formula (formula 1) - referred to as the transmission function - is shown in figure 7。
Only another way to describe the relationship between output and input。
Figure 8. The closed loop system feeds back a portion of its output signal into its input。
Our target is a closed loop system, similar to that described in figures 1 and 6. We can use a more generic feedback expression by drawing a block and naming it beta. We can use the difference input as an internal circle with an x; this is the common symbol of the sum. Pixmap 6, summation is the node that r1 and r2 connect to the negative input of the operator amplifier. The closed loop server system is shown in figure 8。
Some of the terms used are self-evident, while others are not. The following are all terms and their meanings:
So far, decay (beta) represents the ratio of two resisters. Remember that feedback networks may be more complex and complex than two resisters: using diodes, capacitors and sensors, or even having a second operator amplifier in the feedback circuit. In a number of published articles, the term v in addition to -5 - beta is referred to as error voltage (e) or total voltage (cyber)。
The operation amplifier has a limited (but very large) open-ring gain and the thallium voltage is very small. So, very small gills multiplied by very large a-olds give us most of the time outside v, which is exactly what we expected. For signals with higher frequencies (e. G., 10 khz), a is clearly less than straight current or low frequency. This means that output will no longer follow input (albeit with an increase), but will not fully meet our expectations (i. E., a distortion)。
To understand exactly why this is happening, we need to further study mathematical analysis. We'll leave it to my next article to discuss the compute amplifiers。
