DE1537590B2 - Differential amplifier circuit - Google Patents

Description

1 2

The invention relates to a differential amplifier - no common mode current from the first point to the

circuit. two other points through the differential

The two input connections of the differential stronger. For example, with the mentioned

Amplifiers are symmetrical to a common computational amplifier to ensure that over

Point that belongs to the amplifier. This common 5 the input resistances are not unbalanced

The point is often earth or mass. That to strengthen- currents flow more.

The signal is between the input terminals. Practically, the common mode signal now appears on created. If two different signals are connected to each other amplifier output, since the equalization signal compared the are to be fed, they are fed between the overhead connections, however, that is common Point and one of the input connections io ratio of the amplified useful signal to common mode applied separately. signal now improved by a factor equal to the

When a signal between the common point is amplification of the amplifier. In addition, can and each of the input terminals is connected at the same time, the output impedance of the amplifier is very low then this signal will form a common mode signal, e.g. B. 1 Ω, and the input resistances called. A common mode signal can be in a source 15 of a differential arithmetic amplifier connected downstream one applied between the input connections can be selected to have a corresponding high resistance, see above Signals arise when the internal impedance of that any asymmetry is practically negligible Source not relative to the common point sym- and the common-mode signal at the output of this post-metric is. When a differential amplifier further switched amplifier can be easily suppressed not completely sysmmetrical in relation to the common 20 can.

The same point (symmetrical to the earth) is formed, as has been mentioned above, it can be at the

an attenuated common-mode input signal at the amplifier seems to be an arithmetic amplifier, and

Output of the amplifier, even if the input, it can also have several current transfer stages

signal source is symmetrical. (also emitter-coupled or collector-coupled

If the differential amplifier contains 25 push-pull stages) with field-effect transistors, for example, an arithmetic amplifier with ren or conventional transistors, furthermore an input resistance in each input circuit called "transistors",
and two feedback resistors are involved, and the terms "cathode", "anode" and "control the amplifier have a high input impedance connection" are generally used here instead of, the input resistances can, for example, 30 current output connection (source) and emitter connection, a nominal value of 1 Have ΜΩ. The value of this suction electrode connection (sink) and collector connection resistances can differ by about 10 kΩ. Connection and gate and base connection of field effects, so that transistors and transistors caused by the common mode signal are used. The transients and currents flowing through these resistors interfere and field-effect transistors will continue to generate unwanted input signals, which are also referred to as active components,
in the same order of magnitude as the useful signal. The diversion amplifier can be the one that is to be amplified. Since a complete isolation amplifier with amplification factor Han symmetry cannot be developed in practice, a first common-mode interference signal at the output between the cathodes is unavoidable. takeover stage and the anodes of a second power

The object of the invention is therefore that the takeover stage is switched. The control connections

see, the common-mode signal suppression in the case of a third current transfer stage, the active construction of which

to improve potential amplifiers. elements are connected as a cathode follower, and the

According to the invention, this object is formed by the amplifier output stage, can be achieved with the fact that an anode, which is permeable in the amplification direction, of the active components of the second current isolating circuit is connected on the input side to a first point 45 transfer circuit,
The differential amplifier circuit, at which only common-mode signals appear at the output during operation, and via the cathode follower in the first current transfer side with two further points of the circuit, via the amplifier with amplification, between which the operating factor is connected during operation and via the cathode follower in which a differential output signal occurs, and that the ver 50 is supplied to the third current transfer stage.
Strengthening from the first point to the two other A fourth current transfer stage with two active points via the isolating circuit is equal to one. Components can be in the anode circuits of the active

So that the output signal is largely identical to the components of the first current transfer stage Is common mode signal, the equalization signal must be switched to a difference between the ampli if the common mode signal is a direct current component of the common mode signal at the control connections component contains, also a direct current component and cathodes of the active components of the first contain that largely reduce the current transfer stage in terms of amount and sign. The control of the direct current component of the common mode connections of this fourth current transfer stage are equal signals, and if the common mode signal is an alternating signal with each other and via another isolating amplifier contains self-current component, the compensation signal 60 with amplification with the cathodes of the active building must also contain an alternating current component, connect elements in the first power take-off stage The amplitude is largely equal to the amplitude in order to further increase the common-mode signal rejection improve the AC component of the common mode signal.

and which are largely in phase with the alternating current The two isolating amplifiers can be connected in series

component of the common mode signal. 65 switched, whereby the first mentioned separator

Because the through a common mode signal and the amplifier between the output of the other isolating equal signal caused potentials of the input amplifier and the anodes of the two active components and output connections are largely the same, flows elements of the second current transfer stage.

3 4

Embodiments of the invention will now arise on part of the amplifier, which is described in more detail by the one hand of the drawings. input resistances .R ₁ and R _{1 is} formed as a result

In the drawings is: an inequality of ^ ₁ and A ₁ 'or an in-

F i g. 1 is a block diagram of a circuit with symmetry in one to the input terminals 11 and

A differential amplifier, 5 12 connected source, is shown in FIG. 2 shown. here

Fig. 2 is a circuit diagram of an inventive amplifier stages 10 together with the

Differential amplifier and resistors A ₁ , R ₁ , R ₂ and R ₂ ' as well as the input

3 shows a circuit diagram of a further embodiment of input and output connections 11, 12, 16 and 17

a differential amplifier according to the invention. shown.

The differential computing version shown in FIG. 1 The amplifier will first be described. A first

stronger contains one or more amplifier stages 10, current transfer stage contains two field-effect transitions

Input resistances R ₁ and R ₂ ', feedback disturbance 18 and 19, the cathode terminals 5 with a

resistors R ₂ and R ₂ ' and input terminals 11 constant current source and its anode terminals D

and 12. The signal to be amplified comes from one with two loads 21 and 22 are connected.

Source 13, which is between the input connections 15 This current transfer stage amplifies the connection

is, and a common mode input signal from a sen 11 and 12 supplied signals and leads them to a

Source 14 to the input terminal 11 and via the second current transfer stage, which the transi-

Source 13 is supplied to input terminal 11. At the disturbing 23 and 24, a constant current generator 25

The output of the amplifier is a consumer 15. and contains the resistors R ₃ and R ₃ ' . Two more

For the output current of the current source 14 there are 20 with resistors R _i and i? ₄ 'as a cathode follower

four circuits: switched on transistors 26 and 27 amplify this

1. Via the resistors .R ₁ and R ₁ , and the collectors of the transistors 23 and 24 load 15 to ground nende signal and lead it to the terminals 28 and

2. via the resistors R ₁ and R ₂ and the circuit 29 to. Since between the terminals 11 and 17 and consumers 15 to ground 25 between the terminals 12 and 16 no reversal

3. is done via the resistor ^ and the amplifier, the feedback resistors R ₂ and step 10 to the output terminal 16 and R ₂ between the terminal 16 and the control

4. Via the resistor R ₁ and the amplifier connection of the field effect transistor 18 and the stages 10 to the output connection 17. Terminal 17 and the control connection of the field effect transistor

The transistor 19 is switched from the current source 14 via the resistors 30 to the amplifier

A ₁ and R ₁ flowing current calls a voltage on to act as an arithmetic amplifier.

Input of the amplifier stages 10 emerges when this The common mode signal is the input terminals

Resistances are not exactly the same. These additional 11 and 12 are supplied and practical as with one

borrowed input voltage can be large in relation to the cathode follower without significant change in the am-

Signal from source 13 if it is for example 35 plitude and phase position and size and polarity of

wise for the resistors, R ₁ and A ₁ 'by 1-ΜΩ- the control connections of the field-effect transistors 18

Resistors and at resistors R ₂ and R ₂ ' and 19 transferred to their cathode terminals. A

is ΙθΟ-ΜΩ resistors, since an unbalanced isolating amplifier 30 with a gain factor of 1

trie of, for example, 10 kΩ between the cons the common-mode signal is practically also without

would be R ₁ and A ₁ 'and a significant change in amplitude and phase or

Common mode voltage of only 10 mmV one input size and polarity to the collectors of the transi-

voltage of microvolts. disturb 23 and 24. In this way an

A signal from the source 14 via the resistors R ₁ and equal signal, which essentially corresponds to the common mode

A ₁ 'flowing current can be suppressed as a result, the signal is identical to the output connections.

the one that leads to the output terminals 16 and 17 of the 45, from the collectors of the transistors 23

Amplifier a compensation signal is applied, which and 24 are formed, and the amplifier 30 is used

is identical to the common mode signal. If it turns out to be a diversion device as it is a diversion for

For example, in the case of the common-mode signal, the common-mode signal with respect to a part of the

DC signal acts, there is no voltage that represents a differential amplifier. From there it reaches the

which drive a current through the resistors R ₁ 50 connections 16 and 17 through the cathode follower

would, since the compensation signal at the terminals 16 effect of the transistors 26 and 27, again far-

and 17 in terms of magnitude and sign the same as going without changing the amplitude and phase

Common mode signal at terminals 11 and 12 is. or size and polarity. The isolation amplifier 30

Although the common-mode signal is the input it allows the cathode connections of the field connections of the consumer 15 to be fed, but 55 effect transistors 18 and 19 are connected to the collectors, which is the ratio of the amplified output signal of the transistors 23 and 24, without amplifier stages 10 to the Common mode signal improved. that the high impedance of the constant current source 20 Since this ratio is also shunted by a factor. The internal resistance of the current source is improved, which is equal to the gain of the amplifier 20 should be as high resistance as possible so that kers is, and since the output impedance of the amplifier 60 can be kept practically 100% of the common mode signal to the isolating stage 10 low, e.g. B. to amplifier 30 are fed.
1 Ω, is the common-mode rejection at the consumer. The common-mode rejection in the amplifier according to FIG. 2 can be improved even further if the consumer is dealing with a further amplifier, since any asymmetry in the control element is relatively easy to influence. 65 electrode-anode capacitance of the field-effect transistor

One possibility, the output connections Ausren 18 and 19, the influence of some asymmetry

to supply DC signals in order to suppress the output resistances and capacitances

To improve common-mode signals that are connected to earth or ground in that of their control connections

can be wrestled. The current flowing through these capacitances as a result of the common-mode signal can flow through Application of the common mode signal to the anode connections of these field-effect transistors is reduced will. For example, an amplifier with a gain of 1 can be placed between the connected anode connections the field-effect transistors 18 and 19 and the connected base connections of the other two Transistors are switched, the anode connection of each field-effect transistor being the Contains emitter / collector path of one of the other transistors. That way, that's already going on common-mode signal present at the cathode connections of the field-effect transistors to their anode connections fed.

Since the common mode rejection in the amplifier according to FIG. 2 and the mentioned modification of this Amplifier depends on the equalization signal being largely equal to the common mode signal as an amplifier with a gain factor of 1 cathode follower be used.

The cathode follower effect of the field-effect transistors 18 and 19 is achieved by inserting further transistors further improved in their anode circuits.

The amplifiers with gain factor 1 can be used in Can be connected in series as shown in FIG. Here an amplifier connects with a gain factor 1, a field-effect transistor 32 connects the cathodes of the field-effect transistors 18 and 19 to the Base connections of two transistors 33 and 34, which are connected to the anode connections of the field-effect transistors 18 and 19 are connected. That which appears at the cathode connection of the field-effect transistor 32 Common mode signal is passed to amplifier 30, which is shown by a dashed line and contains two transistors.

The output signal of the amplifier 30, which, as already mentioned, has a gain factor of 1, is then fed as a compensation signal to the collectors of transistors 23 and 24 via a Zener diode 35.

Another amplifier stage between transistors 33 and 34 and transistors 23 and 24 is formed by transistors 36 and 37.

Those components in FIG. 3 which have the same functions as the components according to FIG. 2 have are provided with the same reference numbers. The function and mode of operation of the other components according to F i g. 3 are familiar to the person skilled in the art.

A capacitive asymmetry in the input circuit of the amplifier according to FIG. 3 can also be set on a differential capacitor 38 between the collectors of the transistors 33 and 34 lies.

Although described with reference to FIGS Embodiments of solid-state components with a cathode, an anode and a control terminal are used, circuit arrangements can also be built in which Thermionic vacuum tubes are used, all of which have a cathode, an anode and a control connection to have.

Claims (6)

Patent claims: 1. Differential amplifier circuit, thereby characterized in that an isolating circuit (30) permeable in the amplification direction on the input side with a first point of the differential amplifier circuit at which during the Operation only common mode signals occur, and on the output side with two other points of the circuit is connected, between which a differential output signal occurs during operation, and that the gain from the first point to the two other points via the isolating circuit (30) is equal to one. 2. Circuit according to claim 1, characterized in that it has a first current transfer stage with active components (18, 19), each with the input connections (11 and 12) the differential amplifier circuit are connected, and contains a second current transfer stage, wherein the isolating circuit (30) between the common branch (20) of the first current transfer stage and the output connections of the active components (26 and 24) of the second current transfer stage lies. 3. A circuit according to claim 2, characterized in that two further active components (23 and 24) each with the anodes, collectors or sinks of the active components (18 and 19) of the first current transfer stage are connected and from a further amplifier (32) are controlled, which is connected to the common branch (20) of the first current transfer stage is. ' 4. A circuit according to claim 2 or 3, characterized in that intermediate amplifier stages (36 and 37, 26 and 27) between the two current transfer stages and between the second current transfer stage and two output terminals (28 and 29) are connected. 5. Circuit according to one of claims 1 to 4, characterized in that feedback impedances the input terminals (11 and 12) connect to the output connections (28 and 29). 6. Circuit according to one of claims 1 to 5, characterized in that the active components Are solid-state components. 1 sheet of drawings