[introduction] circuit of an individual test but ” all standard DC that carries out place of comprehensive to any operation amplifier examination to need checks ” . Individual test circuit may be used quite at that time, but be not today such, because contemporary operation amplifier has more comprehensive standard. Accordingly, individual test circuit undertakes the whole thing no longer all DC check.

Circuit of an individual test but ” all standard DC that carries out place of comprehensive to any operation amplifier examination to need checks ” . Individual test circuit may be used quite at that time, but be not today such, because contemporary operation amplifier has more comprehensive standard. Accordingly, individual test circuit undertakes the whole thing no longer all DC check.

Often use develop of circuit of 3 kinds of tests to attack now to operation amplifier DC parameter undertakes workbench and production check. These 3 kinds of develop attack for (road of annulus of test of amplifier of 1) double operation, (2) tests annulus way oneself (say breakdown sue for peace chooses test annulus route sometimes) and (3 operation of 3) amplifier annulus road. You can use these circuit to check DC parameter, include static electric current among them (IQ) , voltage is maladjusted (VOS) , power source is restrained than (PSRR) , in all the model is restrained than (CMRR) and gain of DC open loop (AOL) .

Static electric current

Static electric current is to show parts of an apparatus outputs electric current to be equal to the electric current that its spend zero hour. Although IQ test looks quite simple, but also must notice to ensure favorable result, when handling part of extremely tall or extremely low IQ especially. Graph 1 it is to be able to use 3 kinds of of test IQ and other parameter practical circuit, its must consider a certain number of load current cases. This includes to check the feedback electric current in annulus road. Actually, rf also can give feedback resistor parts of an apparatus bring load, influence IQ is measured.

Graph these 3 1 circuit are usable will measure static electric current (IQ)

We are with checking OPA369 operation amplifier exemple will show these circuit. The static electric current of this component is every passageway 1 μ A. Input maladjusted voltage to be 750 μ V. Graph circuit of amplifier annulus road can be 1 medium double operation to be offerred by the output of test parts of an apparatus the voltage of 750.75mV. Voltage of this kind of input can make Rf carries the electricity of 15 μ A. This electric current comes from power source, can give any measurement to increase an error. Before undertaking IQ is measured accordingly, must adopt measure to ensure output electric current is equal to really 0.

Testing circuit oneself is not the effect circuit that measures electric current of extremely small static state, because output must provide feedback electricity. In should carry out a process, maladjusted VOS adjusts the voltage after output needs fibrous root occupies gain (be not easy thing) , perhaps need to disconnect the 50 Ω resistor that above principle pursues medium, in order to eliminate feedback electric current. Double amplifier annulus road can achieve 0 output to ask through increasing another amplifier. Elaborate choice low input slants amplifier of road of annulus of buy electric current, the error that can make output electric current to arise is very small.

In addition, annulus road also can help 3 operation amplifier you measure IQ, but the 1M Ω resistor that should notice parts of an apparatus be metricaled outputs end, this will become an issue, because no matter which measure,be planted parameter, it always is load of a parasitism. If measure output load current, this resistor represents an add load. In addition, return the noise issue that must consider this resistor, the noise that issues 1M Ω resistor to the frequency of 10kHz in 0.1Hz is 85 μ Vp- P. Resistor of use 100k Ω can reduce noise to 27 μ Vp-p. Accordingly, reduce resistor value to be able to reduce noise, but the parasitism resistor load that output of parts of an apparatus be metricaled carries is met subsequently more apparent.

Voltage is maladjusted

VOS test is the base that measures parameter of technology of DC of other of operation amplifier great majority. Because this wants to notice to test circuit all the more, the circuit when checking other parameter in order to ensure also can good job. If did not choose good to should check configuration, meeting influence is measured to other DC.

The definition means of VOS has a variety of, familiar pattern includes: “The DC needing branch that place of 0 output voltage offers to need when do not have input signal or having power source resistor inputs voltage ” (reference material 2) , or ” in either input end comes the poor cent DC that signal and resistor input to offer place of 0 output voltage to need for zero hour without other in the method of ground connection inputs voltage ” (reference material 3) . Means of another kind of definition is ” slant in the input the DC needing branch that buy electric current outputs end to offer 0 voltage place to need in operation amplifier for zero hour inputs voltage ” , this is to measure the ideal and academic method that inputs maladjusted voltage, do not have practice sense, because 0 inputs slant,the operation amplifier of buy electric current does not exist.

According to above definition, you already but the alterable voltage power source of will low output, high accuracy, high resolution joins the input to operation amplifier is carried, voltage of adjustable also input, till output voltage is 0. So inputting maladjusted voltage is voltage of place application input only choose instead.

This kind of method is put in two serious problems. When the test has the operation amplifier of gain of extremely tall open loop, must ensure the resolution of voltage power source is less than ability of 1 small bend over to assure to achieve aleatoric rate but repeatability. In addition, still must use iteration to be close to a law to make output voltage for 0. Meeting coupling goes to the noise in the system in voltage power source and operation amplifier, the measurement that makes high speed automation checks an environment to fall and control cannot come true almost.

Graph 2 use this circuit to measure voltage maladjusted VOS

As a result of these problems of good method, because this checks the place below the environment in workbench,the commonly used method of the choice is will be put in turning over photograph gain to configure by test parts of an apparatus, if pursue,2 are shown. The advantage of this kind of method depends on be being checked not only parts of an apparatus is very stable, and do not need additional compensation normally.

In addition, test circuit still may need to be in blame resistor of a 50 Ω is offerred between input and ground connection instead, in order to offset the input slants buy electric current. Nevertheless, slant to the input the operation amplifier with buy extremely small electric current, of this resistor true ” contribution ” increase noise namely. To the parts of an apparatus of 100pA, when doing not have this resistor, add error has 0.005 μ V only. This kind of quits action is in only slant the ability when the direction of buy electric current and volume level are equivalent is effective.

Graph 2 medium circuit are a graph 1 in what choose a method from test sue for peace is brief, but without resistor R1 and R2. This circuit has inherent stability to most operation amplifier, its normally but crushing any potential inadequacy, those who make make test circuit.

If use a figure,2 medium test circuit undertake other checks, its defect can be shown. For example, graph 2 medium circuit are met wait for other parameter to produce an effect to measuring IQ and AOL.

This kind not the circuit of drive can cause VOS error, error value is equal to (gain of VOS* closed circuit) * AOL(unit is V/V) . This error may not matter, also can make through applying proper VIN VOUT is reduced for 0.0V.

Can use formula of the following computation the 1 output that adjusts place to need to output carries an error to compensate formula.

Formulary 1:

Ideal of VOUT= (2 * ASJ+ ACL- ASJ) * VOUT()

Among them ASJ is gain of point of sue for peace, ACL is closed circuit gain.

Can use an add amplifier in testing annulus way normally, if pursue,place of road of 1 pair of amplifier annulus is shown. This kind of configuration is close to the requirement that VOS defines. Be maintained to be in by the output of test parts of an apparatus annulus road amplifier comes in the VOS of ground connection. If annulus road amplifier supports VOS adjustment, or you can turn over photograph input to eliminate through control blame maladjusted, what need not be in charge of annulus road amplifier is maladjusted. Adopt this kind of method, you can make be by the output of test parts of an apparatus 0. The voltage that in VOUT end measures is 1001*VOS. Unless laden join comes to be carried by the output of test parts of an apparatus, should output otherwise must offer input of annulus road amplifier to slant only buy electric current. When measuring static electric current, this to low IQ component character is an essential note. In two circuit in front, must be spread feedback report offer Rf by test parts of an apparatus.

Come through inputting the blame of annulus road amplifier join instead but power source of process designing voltage, the other performance data of measurable operation amplifier, for example amplitude of AOL, output and CMRR. Because annulus road controls voltage is change, because this is checked,the output of parts of an apparatus can try to match with control voltage.

Attention, annulus road has double amplifier the following defect:

More complex than testing circuit oneself; needs annulus road compensation, because circuit itself does not stabilize; ,can be in only of annulus road amplifier control inside modular limits in all by the output of test parts of an apparatus.

If annulus road did not receive proper compensation, circuit is met oscillation. You can be passed with Rf paralell connection a proper capacitor stabilizes annulus road. Amplifier of the road that it is annulus decorates proper RC combination to also can stabilize annulus road. We will discuss this annulus road to compensate a problem in the following article.

The form of a kind of change of law of annulus road test is double amplifier 3 amplifier annulus road, its can realize the control that to be being checked parts of an apparatus exports voltage through voltaic guiding. The compensation of this annulus road can pass the RC combination of amplifier of road of the 2nd annulus to undertake installing. Like be in circuit of double operation amplifier, be checked the voltage of parts of an apparatus is maladjusted also be in VOUT end is measured, and VOUT is 1001 times voltage is maladjusted. This circuit develop attacks of before can be being solved one kind of circuit by problem of limitation of amplitude of output of test parts of an apparatus. If need bigger output amplitude, can reduce the resistor that controls voltage series with annulus road.

Attention, annulus road puts 3 amplifier in following defect:

More complex than other circuit; needs annulus road compensation, because circuit itself does not stabilize; ,always be had by the output of test parts of an apparatus the load of 1M Ω .

Power source is restrained than

PSRR is the ratio that change of power source voltage and operation amplifier input maladjusted voltage to change. Simple for, it is the capacity that operation amplifier controls power source voltage to change inside specific limits. Because need maladjusted voltage to finish,should measure, accordingly you can use existing technology to measure VOS. Graph Ludouke uses annulus of 1 medium 3 kinds of tests to finish PSRR to measure. The method is power source + VS and – VS setting is by the power source voltage of test parts of an apparatus, measure 1001*VOS. Next, power source voltage the setting is by the voltage of test parts of an apparatus, measure 1001*VOS again next. Formulary 2 with formula the 3 computational methods that are PSRR.

Formulary 2:

Formulary 3:

When using this kind of method, some operation amplifier needs to consider other factor. These operation amplifier have enough low working voltage, the intermediate dot of power source (0 in all modular voltage) can exceed low power source to configure operation amplifier what what allow is big in all modular voltage. Some course input parts of an apparatus to many input class to course, can work smoothly below this kind of condition, but they can be changed to different input level, cause PSRR computation error. In these two kinds of amplifier, fixed in all modular voltage can prevent in all modular saturation or input class changeover. These two kinds of measurement technique that check for PSRR keep constant in all modular voltage, meeting generation can be calculated in PSRR the quits mistake in the process. What place of these parts of an apparatus need is actual in all modular voltage attacks the develop that inputs class according to amplifier to change and change.

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