Method for optimizing the impedance of a connecting element

Abstract

A method for optimizing impedance of a connecting element between a first component and a second component of a high-frequency apparatus. The first component and the second component have at least two level states, wherein the connecting element has an input impedance and an output impedance. The first component has respective impedances in each of the at least two level states, wherein the second component has respective impedances in each of the at least two level states. The method comprising the steps as follows: determining a respective magnitude of a difference of the first component between the complex conjugated input impedance and a respective impedance of the first component, determining a respective magnitude of a difference of the second component between the complex conjugated output impedance and a respective impedance of the second component, and simultaneously minimizing the respective magnitudes of the first component and second component relative to the in- and output impedances of the connecting element.

Claims

1. A connecting element for optimizing impedance between a first component and a second component of a high-frequency apparatus, especially a field device, wherein the first component and the second component have at least two level states, comprising: an input impedance and an output impedance, wherein: said first component has respective impedances in each of the at least two level states, said second component has respective impedances in each of the at least two level states; a magnitude of a difference of said first component between a complex conjugated input impedance and a respective impedance of said first component and a magnitude of a difference of said second component between a complex conjugated output impedance and a respective impedance of said second component are simultaneously minimized.

2. The connecting element as claimed in claim 1, wherein: said connecting element includes an adapting structure, which has input- and output impedances; the magnitudes of the first component and the magnitudes of the second component are optimized relative to the input- and output impedances.

3. The connecting element as claimed in claim 1, wherein: said connecting element is embodied as an electrical connecting line.

4. The connecting element as claimed in claim 1, wherein: said connecting element comprises at least one resistor and/or at least one capacitor and/or at least one coil.

5. A method for optimizing impedance of a connecting element between a first component and a second component of a high-frequency apparatus, especially a field device, wherein the first component and the second component have at least two level states, the connecting element has an input impedance and an output impedance, and the first component has respective impedances in each of the at least two level states, and the second component has respective impedances in each of the at least two level states, the method comprising steps as follows: determining a respective magnitude of a difference of the first component between the complex conjugated input impedance and a respective impedance of the first component; determining a respective magnitude of a difference of the second component between the complex conjugated output impedance and a respective impedance of the second component; and simultaneously minimizing the respective magnitudes of the first component and second component relative to the in- and output impedances of the connecting element.

6. The method as claimed in claim 5, wherein: the respective magnitudes are weighted before the simultaneous minimizing.

7. The method as claimed in claim 6, wherein: at least one of the respective magnitudes, which exerts no influence on the optimizing of the input- and output impedances of the connecting element, is weighted with zero.

8. The method as claimed in claim 6, wherein: the weighting of the at least one of the respective magnitudes is determined based on the weighting of the input power and/or the input voltage and/or the input electrical current of the first or second component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

(2) FIGS. 1a-1d four different signal pulses according to the state of the art, wherein the pulses are shown by plotting voltage as a function of time, and wherein the pulses are passed between different components of a field device;

(3) FIG. 2 a schematic circuit diagram of a field device according to the state of the art with twelve components D1-D12;

(4) FIG. 3 two components according to the state of the art, which are connected with one another by means of a connecting line, wherein the connecting line includes a damping mat;

(5) FIG. 4 two arbitrary components according to the state of the art, connected with one another by means of a connecting line with a point F, from which impedances of the components are considered;

(6) FIG. 5 two arbitrary components, which are connected with one another by means of a connecting line, wherein the connecting line has an adapting structure;

(7) FIG. 6 a first graph, which shows input- and output powers for different level states of the amplifier;

(8) FIG. 7 a second graph, which shows input- and output powers for different level states of the amplifier, wherein the level states are weighted by means of a first weighting;

(9) FIG. 8 a third graph, which shows input- and output powers for the different level states of the amplifier, wherein the level states are weighted by means of a second weighting; and

(10) FIG. 9 a circuit of a component embodied as an amplifier.

DETAILED DESCRIPTION IN CONJUNCTION WITH THE DRAWINGS

(11) FIGS. 1 a-d show signal pulses according to the state of the art, which are transferred within a field device between its different components. If a signal is pulsed, the signal pulse is composed of a superpositioning of a plurality of oscillations. The individual signal pulse can be enveloped by a curve, which ideally has the shape of a Gauss curve.

(12) FIG. 1a shows an originated first signal pulse 1a, whose first envelope curve A has a first rising edge A1, a first region with a horizontal portion A2 and a first falling edge A3.

(13) FIG. 1b shows a second signal pulse 1b, which has traveled through at least one component and now deviates slightly compared with the originated signal pulse 1a of FIG. 1a.

(14) FIG. 1c shows a third signal pulse 1c, which has traveled through a number of components and has marked differences compared with the originated signal pulse 1a of FIG. 1a. The third signal pulse 1c includes a shortened amplitude C2, reflections C3, multiple reflections C4 and beats C5.

(15) FIG. 1d shows a fourth signal pulse 1d corresponding to the signal pulse 1c in FIG. 1c with a second envelope curve B, which envelops the signal pulse 1d. Envelope curve B includes a second rising edge B1, a second region with a horizontal portion B2 and a second falling edge B3. The second rising and falling edges B1, B3 are flatter than the first rising and falling edges A1, A3 in the case of the signal pulse 1a of FIG. 1a. Accordingly, the second region with horizontal portion B2 is shorter than the first region with horizontal portion A2 of the signal pulse 1a of FIG. 1a. These changes, which a signal pulse suffers after passing through the components, are, for the most part, attributable to reflections occurring in connecting lines.

(16) FIG. 2 shows a schematic circuit diagram of a field device according to the state of the art with twelve components D1-D12 and their connecting lines 2. The electronic components D1-D12 are implemented in the device series Micropilot ES FMR 5 of the enterprise, Endress+Hauser. The electronic high-frequency components D1-D12 are embodied either as active or passive components. The passive components are, for example, the filters D5, D10, D11, the antenna D2 and subcomponents serving as bias (voltage- or electrical current supply) within the oscillators D1, D3 or the amplifiers D4, D6, D8. Active components are, for example, the oscillators D1, D3 and the amplifiers D4, D6, D8 as well as the mixer D9.

(17) Reflections can occur especially between oscillators D1 and D3, between each two of the amplifiers D4, D6 and D8 and between the mixer D9 and the intermediate frequency stage D12. The reaction of the intermediate frequency stage D12 to the mixer D9 is very small due to the large frequency- and impedance difference, but was detected and should, consequently, be heeded. Furthermore, reflections can occur between each two of the components, such as, for example, the transmitting-receiving separator or directional coupler, D7, the mixer D9, the antenna D2, as well as the filters and their bias D5, D10, D11.

(18) FIG. 3 shows schematically a damping mat G according to the state of the art situated between two arbitrary components E1 and E2 according to the state of the art. Damping mat G lessens the reflections in circuit board integrated, high-frequency, connecting lines. For this, the damping mat G is adhered to the connecting line 2 or applied in the form of a paste on the connecting line 2. Disadvantageous in the case of such damping mats G is the high signal loss. The degree of attenuation corresponds about to the attenuation of the transmitted signal pulse.

(19) FIG. 4 shows two arbitrary components E1, E2 of the field device, which are electrically connected by means of a connecting line 2. Considered from an arbitrary point F on the connecting line 2 are a first impedance Z_E1 and a second impedance Z_E2 of the first and second components E1, E2. Impedance matching at the point F results from
Z_E1=Z_E2*,Eq1
wherein Z_E2* is the complex conjugated impedance of Z_E2. From Eq1 there follows
ReZ_E1=ReZ_E2 and ImZ_E1=ImZ_E2Eq2

(20) Since the equations Eq1 and Eq2 are solvable only for a single frequency and not for a frequency band, the equations must be considered approximately. The approximation equations are
ReZ_E1ReZ_E2 and ImZ_E1ImZ_E2Eq3

(21) FIG. 5 shows the first and second components E1, E2 with a connecting line 2, which has an adapting structure 8A. Adapting structure 8A has an input- and an output impedance 8C and 8D. The first component E1 has a first impedance 8B and the second component E2 has a second impedance 8E. If the first and second components E1, E2 have a number of level states Z1, Z2, . . . , there results for the first and second components E1, E2 for each level state Z1, Z2, . . . , in each case, an impedance 8B_1, 8B_2, . . . of the first component E1 and an impedance 8E_1, 8E_2, . . . of the second component E2, wherein the respective impedances 8B_1, 8B_2, . . . , respectively 8E_1, 8E_2, . . . of the first and second components E1, E2 are known. For an impedance matching of the adapting structure 8A to the first and second impedances 8B, 8E, the input- and output impedances 8C and 8D of the adapting structure 8A must be matched respectively to the first and second impedances 8B and 8E of the first and second components E1, E2. For this, all impedances 8B, 8C, 8D and 8E are considered in the Gauss plane, since they are complex valued. In the Gauss plane, the impedances 8B, 8C, 8D and 8E refer, in each case, to a point, which is established by the real- and imaginary parts of the impedances. For example, for 8B:
8B=Re8B+Im8BEq4

(22) If the adapting structure 8A is connected with the first and second components E1, E2 in such a way that the input impedance 8C of the adapting structure 8A is connected to the first component E1 and the output impedance 8D of the adapting structure 8A is connected to the second component E2, then, according to the impedance matching Eq1,
8B=8C* and 8D*=8EEq5
must be fulfilled simultaneously, wherein 8D* is the complex conjugated input impedance 8C of the adapting structure 8A and 8D* is the complex conjugated output impedance 8D of the adapting structure 8A. This means that the separation TA1 of the two points 8B and 8C* and the separation TA2 of the two points 8 D* and 8E must be simultaneously zero in the Gauss plane.

(23) The difference TA1 between the impedance 8B of the first component E1 and the complex conjugated input impedance 8C* of the adapting structure 8A amounts to:
TA1=(Re8BRe8C)+(Im8B+Im8C)Eq6

(24) The magnitude TA1 of the difference TA1 amounts to
TA1={square root over ([Re8BRe8C].sup.2+[Im8B+Im8C].sup.2)}Eq7

(25) The magnitude TA1 is exactly the separation of the two points 8B and 8C* in the Gauss plane. Analogously, the separation TA2 between the two points 8D and 8E* in the Gauss plane amounts to:
TA2={square root over ([Re8DRe8E].sup.2+[Im8D+Im8E].sup.2)}Eq8

(26) In order to minimize the magnitudes TA1 and TA2 simultaneously, the sum TA of the two magnitudes TA1 and TA2 can be minimized:

(27) $\begin{array}{cc}\begin{array}{c}\mathrm{TA}=\mathrm{TA}1+\mathrm{TA}2\\ =\sqrt{{\left[\mathrm{Re}8B-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8B+\mathrm{Im}8C\right]}^2}+\\ \sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8E\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8E\right]}^2}\end{array}& \mathrm{Eq}9\end{array}$

(28) If the first and second components E1, E2 have, for example, four level states Z1-Z4, the input- and output impedances 8C and 8D of the adapting structure 8A must be matched for all level states Z1-Z4 to the first and second impedances 8B and 8E of the first, respectively second component E1, E2. Thus, there results for the magnitudes TA1 and TA2: TA1_1, TA1_2, . . . , respectively TA2_1, TA2_2, . . . for all level states Z1-Z4. For the total magnitude of all magnitudes TA1_1, TA1_2, . . . , respectively TA2_1, TA2_2, . . . for all level states Z1-Z4, there results:

(29) $\begin{array}{cc}\mathrm{TM}=\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}9-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}9+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}9\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}9\right]}^2}+\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}10-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}10+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}10\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}10\right]}^2}+\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}11-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}11+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}11\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}11\right]}^2}+\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}12-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}12+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}12\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}12\right]}^2}& \mathrm{Eq}10\end{array}$

(30) The total magnitude TM is to be minimized relative to the variables 8C and 8D. The magnitudes TA1 and TA2 can, in each case, only be positive or 0, i.e. an optimizing of an individual magnitude TA1, TA2, . . . in the extreme to the detriment of another magnitude is not possible. The in- and output impedances 8C and 8D of the adapting structure 8A, in the case of which the total magnitude TM is minimum, are the optimum values, in order to obtain a matching of the adapting structure 8A to all level states of the first and second components E1, E2.

(31) Some level states should be advantaged or disadvantaged relative to the other level states. This results from the fact that some level states occur more frequently or less frequently than other level states or that some level states require more power or less power than other level states. For these reasons, it makes sense to weight the magnitudes of the differences of the respective level states.

(32) For illustrating the method for weighting, the level states Z1-Z4 of the component D9 (mixer) are considered. It is for simplification that only 4 level states Z1-Z4 are considered. In each level state Z1-Z4, the component D9 (mixer) has a first input power P_in (D8) and a second input power P_in (D4), wherein the first input power P_in (D8) comes from the component D8 and the second input power P_in (D4) comes from the component D4. On the basis of experience, a certain weighting is selected for each level state Z1-Z4 corresponding to the first and second input powers P_in (D8) and P_in (D4). The level states Z1-Z4, the first and second input powers P_in (D8) and P_in (D4) and the respective weightings are shown for the component D9 in the Table T1.

(33) TABLE-US-00001 TABLE T1 The level states of the component D9 (mixer) level P_in P_in state. (D4) (D8) wt . . . description Z1 0 W 0 W 0 components offline Z2 High 0 W mixer-driver without signal Z3 0 W High signal without mixer driver Z4 High High signal and mixer driver

(34) The component D4, which is embodied as an amplifier, is located neighboring the component D9. Corresponding to the Table T1 of the component D9, a Table T2 can be derived for the component D4. For simplification, three level states Z5-Z7 are considered for the component D4.

(35) TABLE-US-00002 TABLE T2 Simplified level states of the component D4 level P_out I_out state (D9) (D5) wt . . . description Z5 0 W 0 A 0 no signal > no reflection Z6 0 W High amplifier without output power Z7 High High amplifier with output power

(36) In such case, P_out (D9) is an output power of the component D4, which goes to the component D9 and Lout (D5) is the output current of the component D4, which goes to the component D5.

(37) Tables T1 and T2 will now be linked with one another. The linking occurs in the following way: The column of the first input power P_in (D8) of the Table T1 and the column of the output electrical current I_out (D5) of the Table T2 have no influence on the connecting line 2 between the components D4 and D9 and are, consequently, not taken into consideration for the linking. Only the column with the second input power P_in (D4) of Table T1 and the column output power P_out (D9) of Table T2 are taken into consideration for linking Tables T1 and T2.

(38) In order to link the weightings of the Tables T1 and T2, all combinations {P_in (D4), P_out (D9)} of the first input power P_in (D4) and the output power P_out (D9) are considered. Four combinations result: {0, 0}; {0, high}; {high, 0}; {high, high}. The combination {0, high}, for example, means, that the first input power P_in (D4)=0 and the output power P_out (D9)=high. Determinative for linking Tables T1 and T2 is how often the state, second input power P_in (D4)=0, is present, namely exactly two times (level states Z1 and Z3) and, in each case, with a weighting of . Thus, the first factor for first input power P_in (D4) for the combination (0, high) becomes: +=.

(39) Decisive for the second factor is how often the state P_out (D9)=high is present, namely likewise two times (level states Z6 and Z7), once with a weighting of 0 and once with a weighting of . Thus, the second factor for output power P_out (D9) for the state (0, high) becomes: 0+=. Then, the first factor for input power P_in (D4) and the second factor for the output power P_out (D9) are multiplied to produce a total factor: *= 2/6. The weighting for the combination (0, high) thus becomes 2/6. This method is performed for each of the combinations {P_in (D4), P_out (D9)}={0, 0); {0, high}; {high, 0}; {high, high}, so that the following Table T3 with the corresponding weightings results.

(40) TABLE-US-00003 TABLE T3 Linking Tables T1 and T2 level P_in P_out state (D4) (D9) wt . . . Z9 high 0 W 2/6 Z10 0 W 0 W Z11 High High 2/6 Z12 0 W High 0

(41) FIG. 6 shows a first graph 13 with the first input power P_in (D4) plotted on the y-axis and the output power P_out (D9) plotted on the x-axis. Entered in this first graph 13 are the level states Z9-Z12 of Table T3. The level states Z9-Z12 define a region 7A. All level states lying between the level states Z9-Z12 come within region 7A. If the weightings are normalized to one, the following Table T4 results.

(42) TABLE-US-00004 TABLE T4 Weightings of Table T3 normalized to one level state P-In P-out wt . . . description Z9 high 0 W Eq9 (Eq5) Z10 0 W 0 W Eq10 Z11 High High Eq11 Z12 0 W High 0 Eq12

(43) The weightings ascertained in Table T4 are taken into consideration for weighting the magnitudes TA1 and TA2 of the different level states Z9-Z12, in order to determine the total magnitude TM. The weighted total magnitude TM then becomes:

(44) $\mathrm{TM}=\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}9-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}9+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}9\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}9\right]}^2}*0.4+\left(\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}10-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}10+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}10\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}10\right]}^2}\right)*0.2+\left(\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}11-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}11+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}11\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}11\right]}^2}\right)*0.4+\left(\sqrt{{\left[\mathrm{Re}8\mathrm{B\_}12-\mathrm{Re}8C\right]}^2+{\left[\mathrm{Im}8\mathrm{B\_}12+\mathrm{Im}8C\right]}^2}+\sqrt{{\left[\mathrm{Re}8D-\mathrm{Re}8\mathrm{E\_}12\right]}^2+{\left[\mathrm{Im}8D+\mathrm{Im}8\mathrm{E\_}12\right]}^2}\right)*0.0$

(45) The last two magnitudes of the differences are weighted with zero, since they do not contribute to optimizing impedance of the connecting line. In order to obtain a broadbanded frequency band applied for FMCW systems instead of an individual expression
[Re8B_11Re8C].sup.2+[Im8B_11+Im8C].sup.2,(Eq15)
the linear average value of the frequency band or for pulse systems a Gauss weighting around the center frequency is applied. Also other weighting methods are possible here.

(46) FIG. 7 shows a second graph corresponding to the first graph in FIG. 6, however, with a weighting of the magnitudes TA1 and TA2 for each level state. The weighting leads to the fact that the region 7A is subdivided into a number of smaller alternative regions 9A, 9B, 9C. In part, such as e.g. in the case of the component D9 (mixer), simulation values were replaced or supplemented by measured values.

(47) FIG. 8 shows a third graph 15 corresponding to the first and second graphs 13, 14 in FIGS. 6 and 7. Here, the level states are represented not by points but, instead, level state regions 10A, 10B, 100, within which points may lie. The sizes of the level state regions 10A, 10B, 10C are governed by the weighting of the respective level states.

(48) FIG. 9 shows the circuit construction of an amplifier 6M of the field device, such as is implemented for the component D6 or D8 (see FIG. 2). As a further example, the weighting method is applied to the amplifier 6M. In the following, only the terminals of the amplifier 6M are considered. The terminals are a signal input 6E, a signal output 6L, a control voltage 6C and a supply voltage 6F.

(49) Resulting from the operation of this amplifier 6M are five level states Z1-Z5 having, in each case, an input power P1-P5 on the signal input 6E, wherein P1=0 and P4P2. The control voltage 6C can assume the different values U1, U2, U3 as well as the different control electrical currents I1, I2, wherein U2=I2=0.

(50) If one enters the level states Z1-Z5 in a column and the associated input powers P1-P5, control voltages U1-U3 and control electrical currents I1, I2 into the respective rows of the level states, the following Table T5 results for the amplifier 6M.

(51) TABLE-US-00005 TABLE T5 Level states of the amplifier 6M level P U I state (6E) (6C) (6F) description Z1 0 W 0 V 0 A HF-system offline, no reflection Z2 P2 U2 0 A sending of pulses, no receipt Z3 P3 U3 I2 receiving, no sending Z4 P2 U3 I2 sending + receiving simultaneously Z5 P5 U2 0 A expecting receipt of pulses

(52) Based on system theoretical ideas, it makes sense to weight the individual level states Z1-Z5. The weightings of the individual level states are presented in the following Table T6.

(53) TABLE-US-00006 TABLE T6 Weighted level states of the amplifier 6M level P U I state (6E) (6C) (6F) wt . . . description Z1 0 W 0 V 0 A 0% HF-system offline, no reflection Z2 P2 U2 0 A 10% sending of pulses, no receipt Z3 P3 U3 I2 60% receiving, no sending Z4 P2 U3 I2 10% sending + receiving simultaneously Z5 P5 U2 0 A 20% expecting receipt of pulses

(54) In the level state Z1, too little power is present on the input terminals of the amplifier 6M to cause a disturbance brought about by reflections. For this reason, this level state is weighted with zero. The level state Z4 represents a so-called near region, in which the signal from one component can cross over to another component. For reasons of perspicuity, power on the output 6L is not given in above table. Table T6 shows, using the example of an amplifier, how the level states Z1-Z5 can be weighted.

(55) Component D1 represents a pulse oscillator and component D6 a transmitting amplifier. The two components D1 and D6 have a different timing. For this reason, a linked Table T7 between the two components takes the following form.

(56) TABLE-US-00007 TABLE T7 Linking Tables T5 and T6 level U P U I state (D1) (D1) (D6) (D6) wt . . . description Z1 low 0 W low low 0% components offline Z2 low 0 W low high 10% standby Z3 low 0 W high high 40% amplifier, no pulse Z4 high high high high 45% pulse is amplified Z5 low low high high 5% post-pulse oscillator

(57) In such case, U (D1) is a voltage on the component D1 (oscillator), P (D1) the output power of the component D1 (oscillator), U (D6) the control voltage of the component D6 (amplifier) and I (D6) the supply electrical current of the component D6 (amplifier).

(58) The research of this method has surprizingly shown that in the case of an HF-amplifier according to FIG. 9 a low control voltage 6C on the gate of the field effect transistor 6H leads to a smaller reaction, especially a smaller reaction to an impedance change, on the output, whereby the transmission of the amplifier from the output to the input is lessened. Furthermore, this leads to a smaller change of the phase difference on the output between turned on and turned off supply current 6F. Such a circuitry is thus also part of the present invention.