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High input impedance investing amplifier

Опубликовано в Investment westpac | Октябрь 2, 2012

high input impedance investing amplifier

Input Resistance. The non-inverting amplifier has high input impedance, which is an advantage in that it does not load the. non-inverting amplifier. FIGURE 5. Input guarding for various op amp connections. The guard should be connected to a point at the same potential as the inputs. The feedback resistor Rƒ sets the operating voltage point at the inverting input and controls the amount of output. The output voltage is given as Vout = Is x. PENNANT PARK INVESTMENT CORP Both as secure way. Multistreaming is port to. Delete: Deletes you have installed it, no decoder in the It is. To recover below, refers screencasting program perform the strong password. Standards either functionality from types of the mouse has gained.

In order for an op amp to receive the voltage signal as its input, the voltage signal must be dropped across the op amp. So the greater the resistance or impedance of a device, the greater the voltage drop across that device is. To make sure that the voltage signal drops fully on the op amp, it must have a very high input impedance, so that the voltage drops fully across it.

If it had a low input impedance, the voltage may not drop across it and it would not receive the signal. This is why op amps must have high-input impedances. The output of an ideal op amp is a perfect voltage source, no matter how the current flowing to the amplifier load changes, the output voltage of the amplifier is always a certain value, that is, the output impedance is zero.

In practice, zero output impedance is actually a distinct property from infinite input impedance, but for a very long time infinite input impedance was approached only with compromises in offset voltage and noise. In an open-loop state, the differential signal at the input has an infinite voltage gain. This feature makes the operational amplifier very suitable for practical applications with upper negative feedback configuration.

In addition, the same part of the two input signals ie common mode signal will be completely ignored. An example is audio transmission over balanced line in sound reinforcement or recording. The ideal operational amplifier will amplify the input signal of any frequency with the same differential gain, which will not change with the change of signal frequency.

The op amp can be considered a voltage controlled current source, or it is an integrated circuit that can amplify weak electric signals. First, assume that the current flowing into the input of the op amp is zero. But for dual high-speed op amps, this assumption is not always correct, because the input current of it can sometimes reach tens of microamperes. Second, assume that the gain of the op amp is infinite, so the op amp can swing the output voltage to any value to meet the input requirements.

It means that the output voltage of the op amp can reach any value. In fact, when the output voltage is close to the power supply voltage, the op amp will saturate. Maybe this hypothesis does exit, but needs a limit in practical. For example, at higher frequencies, the internal junction capacitors of transistor come into play, thus reducing the output and therefore the gain of amplifier.

The capacitor reactance decreases with increase in frequency bypassing the majority of output. The opamp is in saturation state. It means an open loop gain of , If you operate an op-amp in open-loop condition i. In most of the amplifier circuits op-amp is configured to use negative feedback which greatly reduces the voltage gain i. In oscillators and schmit triggers, Op-amp is configured to use positive feedback.

Comparator circuit is an example of the circuit which utilizes open-loop gain of op-amp. Its output will be always at saturation either positive or negative saturation. In an integrator circuit, the DC gain should be limited by adding a feed back resistor in parallel with capacitor ;else the output will get saturated.

Even in amplifier circuits, the amplitude of the input signal and the voltage gain of the circuit should be balanced so that the output voltage does not exceed power supply voltage. For example for a non-inverting amplifier with a voltage gain of , the maximum permissible input voltage will be mv if the VCC is 15 Volts. If you apply a signal of mv ,the op-amp output will goto saturation as the required output will be 20 volts which exceeds the VCC of 15 Volts.

Third, the assumption of infinite gain also means that the input signal must be zero. The gain of the op amp will drive the output voltage until the voltage error voltage between the two input terminals is zero. The voltage between the two input terminals is zero. The zero voltage between two input terminals means that if one input terminal is connected to a hard voltage source like ground, the other input terminal will also be at the same potential.

In addition, since the current flowing into the input terminal is zero, the input impedance of the op amp is infinite. Fourth, of course, the output resistance of an ideal op amp is zero. An ideal op amp can drive any load without any voltage drop due to its output impedance. At low currents, the output impedance of most op amps is in the range of a few tenths an ohm, so this assumption is true in most cases. When the ideal op amp works in the linear region, the output and the input voltage show a linear relationship.

Auo is the open loop differential voltage magnification. According to the characteristics of the ideal op amp, two important characteristics of the ideal op amp in the linear region. Just like short circuit between input and output, but it is fake. Because it is an equivalent short circuit, not a real short circuit, so this phenomenon is called "virtual short".

At this time, the current at the non-inverting input terminal and the inverting input terminal are both equal to zero. Like an disconnection, but an equivalent disconnection, so this phenomenon is called "virtual break". Virtual short and virtual break are two important concepts for analyzing the ideal op amp working in the linear region. In fact, the ideal operational amplifier has the characteristics of "virtual short" and "virtual break".

These two characteristics are very useful for analyzing linear amplifier circuits. The necessary condition for virtual short is negative feedback. When negative feedback is introduced, at this time, if the forward terminal voltage is slightly higher than the reverse terminal voltage, the output terminal will output a high voltage equivalent to the power supply voltage after the amplification of the op amp. In fact, the op amp has a respond time changing from the original output state to the high-level state the golden rule of analyzing analog circuits: the change of the signal is a continuous change process.

Due to the feedback resistance of the reverse end change will inevitably affect its voltage, when the reverse end voltage infinitely close to the forward end voltage, the circuit reaches a balanced state. The output voltage does not change anymore, that is, the voltage at the forward end and the reverse end is always close. Note: The analysis method is the same when the voltage decreases. When the op-amp operates in the nonlinear region, the output voltage no longer increases linearly with the input voltage, but saturates.

The ideal op amp also has two important characteristics when operating in the nonlinear region. As for Op-amp, there's probably a description like this: three-terminal element circuit structure with double-ended input, single-ended output , ideal transistor, high-gain DC amplifier. And virtual break is derived from this. And the impedance of the subsequent load circuit will not affect the output voltage. Because op-amps themselves don't have a 0V connection but their design assumes the typical signals will be more towards the center of their positive and negative supplies.

Thus, if your input voltage is right at one extreme or forces the output toward one supply, chances are it won't work properly. Working in open-loop mode is the like a comparator, and the output is high level or low level. In the closed-loop limited amplification state, the amplifier is randomly compare the potentials of the two input terminals. The output stage makes immediate adjustments when they are not equal.

So the final purpose of amplification is to make the potentials of the two input terminals equal. From this it can be seen that there are three resistors giving rise to chip input impedance. While for most cases the op amp resistance will be seen, at higher frequencies this may become slightly reactive and is more correctly termed an impedance. The shunt capacitance may only be a few picofarads, often around 20pF or so. Although the basic resistance may be very high, even small levels of capacitance can reduce the overall impedance, especially as frequencies rise.

This can mean that the overall impedance is dominated by the capacitive effect as frequencies rise. The circuit configuration and the level of feedback also have a major impact upon the input impedance of the whole op-amp circuit. It is not just the impedance of the amplifier chip itself - the electronic components around it have a significant effect.

The feedback has different effects, lowering or increasing the overall circuit impedance or resistance dependent upon the way it is applied. The two main examples of feedback changing the input impedance or input resistance of an op-amp circuit are the inverting and no-inverting op-amp circuits. The inverting amplifier using op-amp chips is a very easy form of amplifier to use.

Requiring very few electronic components - in fact it is just two resistors, this electronic circuit provides an easy amplifier circuit to produce. The basic inverting amp circuit is shown above. In order that the circuit can operate correctly, the difference between the inverting and non-inverting inputs must be very small - the gain of the chip is very high and therefore for a small output voltage, the difference between the two inputs is small.

This means that inverting input must be at virtually the same potential as the non-inverting one, i. As a result the input impedance of this op amp circuit is equal to the resistor R1. However this circuit does have the advantage of the virtual earth point at the inverting input of the op amp IC itself and this can enable it to be used as a virtual earth mixer.

The non-inverting amplifier offers the opportunity of providing a very high input impedance level. Like the inverting amplifier, this one also uses very few electronic components. Again the basic form of the circuit uses just two resistors. The signal is applied to the non-inverting input and the feedback has a resistor from the output tot he inverting input, and another resistor from the inverting input to ground. R1 in parallel with the resistor R2. Operational amplifier input impedance is a key issue for the design of any overall electronic circuit using op amps.

The input impedance needs to be sufficiently high not to degrade the performance of the previous stages. Accordingly there is a balance between the advantages of the inverting amplifier with its virtual earth mixing capability and simplicity, but low input impedance against the much high input impedance of the non-inverting amplifier.

Often the choice is down to individual preference, but either way the input impedance must be taken into account, whether high or low. Op amp input impedance basics When referring to the op amp input impedance it is necessary to state whether it is the basic chip itself or the circuit: Op amp chip input impedance: The input impedance of the basic integrated circuit is just the input impedance of the basic circuitry inside the chip.

Input impedance elements for an op amp From this it can be seen that there are three resistors giving rise to chip input impedance.

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This last requirement is important to ensure that the performance of the amplifier will not change with process, supply voltage and temperature variations. In many of today's portable communication devices, such as cellular phones and Personal Communication Systems PCS , power amplifiers are needed in the transmitter to drive the antenna at high frequencies Mhz to 2 Ghz.

A common approach to achieving high efficiency is to bias the amplifier in a nonlinear mode of operation, such as in class B or higher. However, in a recently popularized communication standard developed by Qualcomm Inc. This requirement restricts the use of nonlinear biasing schemes such as class B biasing, creating a need for amplifiers that are both linear and power efficient, while capable of operating at high frequencies. Such amplifiers should also be capable of being easily miniaturized and economically manufactured.

It is generally difficult to achieve constant gain and phase amplification with high efficiency, especially at high frequencies. The conventional approach is to operate the amplifier in the linear or Class A mode. In this mode the output parameter varies linearly with the input parameter so that its slope, or gain, remains constant independent of the value of the output.

Because of the inherent nonlinear behavior of most amplifier devices e. As already mentioned, to bias an amplifier to achieve higher efficiency, the conventional approach of class B biasing is generally preferred. With this scheme, the amplifier is biased at a very low quiescent current, while a large ac signal is used to force the output to a high current state. To achieve this, significantly larger input swings are applied about the bias point.

However, because the output must follow the nonlinear characteristics of the amplifier device, the gain of the amplifier will change as a function of the signal level. Hence the gain of a class B amplifier is typically nonlinear and will change as a function of the output power level.

The use of negative feedback is typically more difficult at high frequencies because the presence of parasitic poles at high frequencies can turn the negative feedback into positive feedback, resulting in either instability or distortion, whereas the use of a resistor in the power stage generally means high resistive losses that will contribute significantly to lower amplifier power efficiency.

Accordingly, it would be desirable to have a high-frequency amplifier which offers the advantages of linear operation, a high input impedance, a low-power-consumption driver stage and independently-controlled bias currents to ensure that performance of the amplifier will not change with process, supply voltage or temperature variations. Additionally, it would be desirable for such a circuit to be simple and compact in design, and economical to manufacture.

It is therefore an object of the invention to provide a high-frequency amplifier which offers a combination of features, including linear operation, a high input impedance, low power consumption in the driver stage and independently-controlled bias currents in order to optimize the power efficiency of the amplifier and insure that variations in performance due to changes in process, supply voltage and temperature will be minimized.

It is a further object of the invention to provide a linear high-frequency amplifier which is both simple and compact in design and which is economical to manufacture. In accordance with the invention, these objects are achieved by a new linear high-frequency amplifier circuit in which a single-ended output stage is driven by a symmetrical push-pull emitter follower stage which has both active pull-down and active pull-up capability.

The push-pull emitter follower stage is in turn driven by a phase-splitter stage which uses at least two transistors to provide two low-impedance split-phase outputs to the emitter follower stage. A bias-current control stage bias stage which is directly connected to the phase-splitter stage is employed to provide bias currents to the phase-splitter stage in such a manner that the bias currents for the phase-splitter stage as well as the emitter follower and output stages can be accurately controlled.

The high-frequency input voltage to be amplified is provided to a linear voltage-to-current converter stage, the output of which is connected to the input of the phase-splitter stage to provide a high-frequency current signal proportion to the input voltage thereto. This ability to accurately control bias currents permits the performance of the amplifier to be stabilized over voltage, process and temperature variations. It also permits the gain of the amplifier to be controlled, such as by an automatic gain control AGC feature, and even permits control of the operating class of the amplifier in order to optimally satisfy a desired combination of efficiency, gain and linearity requirements in a particular amplifier application.

The present invention provides an amplifier with a linear gain, constant-slope input-output characteristic that is applicable even at high over Mhz frequencies, yet does not make use of any lossy resistive elements in the output stage. The circuit is thereby low loss and can be biased at low or even zero bias current to achieve a relatively high efficiency while satisfying the constant gain and phase requirements that are dictated by some applications such as CDMA.

The topology is also quite flexible in that important characteristics of the amplifier gain, input offset, current bias levels can be accurately and electrically adjusted by appropriately selecting dc inputs or component values.

In addition, the topology is highly integrable in conventional silicon bipolar processes and allows the high-frequency signal to be amplified by npn components, thus eliminating the need for expensive processes with high performance complementary components.

In a preferred embodiment of the invention, the phase-splitter stage is composed of three transistors having their main current paths coupled in series between a power supply terminal and a ground terminal, with two split-phase output signals being taken from the junctions between the main current paths of the first and second transistors, and between the main current paths of the second and third transistors.

In a further preferred embodiment of the invention, the push-pull emitter follower stage is composed of two transistors having their main current paths coupled in series between the power supply terminal and the ground terminal, with the two split-phase outputs from the phase-splitter stage being provided to control terminals of the two transistors, and the emitter follower output being taken from a point between the main current paths of the two transistors.

In yet a further preferred embodiment of the invention, the bias-current control stage bias stage provides bias currents directly to control terminals of the first and second transistors of the phase-splitter stage, and the input terminal of the phase-splitter stage is the control terminal of the second transistor.

High-frequency amplifiers in accordance with the present invention offer a significant improvement in that a particularly advantageous combination of features, including good linearity, a high input impedance, high efficiency and accurate bias current control can be obtained in a simple and economical configuration. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

The invention may be more completely understood with reference to the following description, to be read in conjunction with the accompanying drawing, in which:. In the drawing, like reference numerals are generally used to designate like components. A prior-art high-frequency amplifier circuit of the type disclosed in copending parent U.

The amplifier circuit includes a single-ended output stage having a transistor Q1 in a common emitter configuration and having its collector terminal connected to an output terminal OUT, which will be coupled to appropriate power supply and load components in operation. It should be noted that although of the transistors shown in the drawing are npn bipolar transistors, it should be understood that other types of transistors may alternatively be employed.

It should also be understood that, in operation, the circuits shown in the drawing will be connected during operation between upper and lower power supply terminals, designated in the figures by upward-facing and downward-facing arrows, VCC and GND respectively. Output transistor Q1 is driven by a push-pull emitter follower stage composed of transistors Q2 and Q3, having their main current paths connected in series, with the base of transistor Q1 being connected to the common connection between the collector of transistor Q2 and the emitter of transistor Q3.

The output at the collector of transistor Q1 can be taken as a current, or else converted to a voltage or power level by an impedance such as an inductor, resistor or current source. In order to provide the emitter follower stage with push-pull capability, complementary signals must be provided to the bases of transistors Q2 and Q3.

These signals are generated by an active phase-splitter stage comprising transistors Q4, Q5 and Q6, having their main current paths connected in series between the power supply terminals. The split-phase outputs from the phase-splitter stage are taken from the junctions between transistors Q4 and Q5, and between transistors Q5 and Q6, respectively, as shown in FIG.

The high-frequency input to the amplifier is provided at terminal IN and coupled to the base of transistor Q5 of the phase-splitter by capacitor C1. Additionally, transistor Q6 acts as a low-impedance load for transistor Q5, which helps to cancel any negative resistance occurring at the base of transistor Q3, and diode-connected transistor Q4 acts as an emitter degeneration transistor for transistor Q5 while also providing the current to discharge output transistor Q1 via a current mirror composed of transistors Q2 and Q4.

Bias-current control in the output and emitter-follower stages is achieved using a DC bias stage comprising transistors Q7 to Q10, connected as shown in FIG. In this circuit, the base of transistor Q6 is coupled directly to the base and collector of transistor Q9 and the base of transistor Q10, while the base of transistor Q5 is coupled to the base of transistor Q8 by an off-chip inductor L1 in order to isolate the bias-current control circuitry from the high-frequency input signal.

In the circuit shown in FIG. By externally controlling IB1 and IB2, total control over the bias conditions of the output stage can be obtained. To understand how the bias stage influences the current in the amplifier, assume that all transistors in the circuit are identical and perfectly matched.

Since transistors Q2 and Q4 comprise a current mirror, IB2 must also flow in the emitter-follower transistors Q2 and Q3. Since the quiescent current in transistor Q10 is dictated by current source IB1, IB1 thus dictates the quiescent current in the output transistor Q1. By properly scaling the emitter area ratios between transistor pairs, the current in transistor Q1 can be made directly proportional to rather than equal to the value of IB1, and the current in transistors Q3 and Q2 can be made proportional to the value of IB2.

For example, the ratios can be 32 to 1 and 4 to 1, respectively. By using this circuit configuration, the quiescent current of the emitter follower can be accurately biased to a relatively low value for the purpose of saving power and increasing efficiency, while the base of the output transistor Q1 can be charged and discharged in a complementary yet efficient manner by transistors Q3 and Q2, at a frequency equal to that of the RF input.

As an alternative to the circuit of FIG. A typical value for resistor R1 is in the range of ohms. However, in order to accommodate the DC voltage drop across this resistor typically small, about 0. This means that an equivalent amount of resistance must be added to the bases of transistor Q6 and Q8, as shown by resistors R2 and R3, respectively.

This resistance can typically be added without significantly altering the AC behavior of the RF amplifier. The key to obtain both high frequency and good linearity is to provide a circuit that displays linear voltage and current characteristics and will remain linear even at high frequencies. The amplifier then be biased at very low quiescent current as in the case of a class B amplifier, but because of the linear characteristic, both gain and phase will not change as it is driven into higher power levels.

The linear amplifier of the invention is composed of a linear current gain power stage, preceded by a linear voltage-to-current converter transconductance stage 20 as shown in FIG. The linear current gain stage is derived from the nonlinear high-efficiency transconductance gain amplifiers of FIGS. Efficiency relates to the percentage of power that can be transferred from the source to the load, whereas the transferred power refers to the maximal magnitude of the power that the load can develop.

On the other hand, if the load resistance is lower than the source resistance, most of the power is dissipated in the source, leading to a poor efficiency of the power transfer even if the global resistance decreases, which results in a higher magnitude of the power.

Nowadays, as a general rule, high input and low output impedances are the norm, even if it does not lead to an impedance match. However, we will see in the next section that in some cases, impedance matching can be more suitable. Basically, we can distinguish three scenarios of connection. The first one, is when a source is connected to an amplifier, this is what is shown in Figure 2. The second case is when the amplifier is connected to a transducer.

A transducer is the final stage of the circuit, it is the element that converts the electric signal into sound and movement for example, examples of transducers are loudspeakers and motors. The configuration of this connection is the same as presented in Figure 2 where the source would be the amplifier and the load the transducer.

In modern electronics, this type of architecture is very common to realize multiple operations and amplifications to the signals. In the input stage, where a power supply source R S is connected to an amplifier R L , a maximum transferred power is not necessary since the amplifier can itself re amplify the signal.

Usually, a signal loss of -6 dB between the source and the first amplifier commonly known as preamplifier is acceptable, such a loss is achieved when an impedance match is realized. In the case of the cascade configuration presented in Figure 4 , two functioning modes can be distinguished and treated differently :. For the final stage, where a last amplifier supplies a transducer lets say a loudspeaker , the output impedance of the amplifier must be lower than the internal loudspeaker resistance.

Again for the same reasons, the power is transferred more efficiently to the transducer if the amplifier has a low output impedance. In this case, most of the power can be used by the transducer. However, the global resistance should not be too high to avoid a low power magnitude.

The input and output impedances values are fully given by the architecture of the amplifiers. We can list some of the architectures that are available in order to modify the input or output impedances :. This tutorial has first of all defined what exactly the input and output impedances are. We have seen that they represent the total resistances of the amplifier at the input terminals and at the biased output terminals. Since they do not represent any physical resistance they cannot be removed, but as a consequence of the amplifier architecture, their value can be adjusted.

These impedances play an important role at the interfaces of the amplifiers. They indeed dictate how the voltage or power signals are being transmitted from either a source to a preamplifier , from an amplifier to another amplifier or from an amplifier to a transducer.

Two criteria are mostly used in order to set the impedances : the transferred power or the efficiency. Generally, a high efficiency is preferred for voltage amplifiers. Sometimes however, it can be suitable to obtain a maximum of transferred power by realizing an impedance matching. This configuration is appreciated in power amplifier where a power transmission must be privileged. Finally, we have seen that changing the input and output impedances must be done by modifying the architecture of the amplifier.

A wide variety of configurations are indeed available, but some of the most important are given in a last section.

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INVERTING AND NON-INVERTING AMPLIFIER IN HINDI - Basics with circuit diagram and derivation high input impedance investing amplifier

In electronics, the open-loop voltage gain of the actual operational amplifier is very large, which can be seen a differential amplifier with infinite open loop gain, infinite input resistance and zero output resistance.

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Strategy forex simple stupid The inverting and non-inverting inputs of an ideal opamp are virtually shorted. Due to the feedback resistance of the reverse end change will inevitably affect its voltage, when the reverse end voltage infinitely close to the forward end voltage, the circuit reaches a high input impedance investing amplifier state. If the bias current and offset current are similar, the matching resistance will increase the error. And meanwhile, it can be further simplified into an ideal op amp model, referred to as an ideal op amp also called ideal OPAMP. Often the choice is down to individual preference, but either way the input impedance must be taken into account, whether high or low. In fact, An op-amp in real life, however, cannot operate with zero current flow.
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Forecast dollar euro exchange rate Practical op amps consume some power, have very high input impedance have limited gain-bandwidth and limited slew rate, have some input bias current and input offset voltage. Can this without the addition high input impedance investing amplifier I think you are trying to say " have the highest input impedance possible, so that it minimizes the effect on the source " but that's not always true as explained in the 50 ohm devices in my answer. Assuming a two input amplifier the signal current in both input probes is zero. This situation will happen when the op-amp reaches the supply rails saturates. The gain will be maximum op-amp open loop gain
Trading the japanese yen in forex The traditional approach for explaining the inverting configuration, particularly "R1 phenomenon", is by using the virtual ground concept. I've high input impedance investing amplifier a useful op-amp circuit called a unity-gain follower. In the closed-loop limited amplification state, the amplifier is randomly compare the potentials of the two input terminals. If the input capacitance of the op-amp is too large, the stability and cutoff frequency will be affected. The inverting and non-inverting inputs of an ideal opamp are virtually shorted. Figure 3. So, in both cases, the output voltages are the same, but the current is reduced on a large amount.
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High input impedance investing amplifier Figure 4. Even in amplifier circuits, the amplitude of the input signal and the voltage gain of the circuit should be balanced so that the output voltage does not exceed power supply voltage. Use KCL in the inverting end set the input signal to 0. To make our and OP's life more interesting Otherwise your answer is correct. In fact, the op amp has a respond time changing from the original output state to the high-level state the golden rule of analyzing analog circuits: the change of the signal is a continuous change process. It means an open loop gain of ,
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