DE102010014101A1 - Hybrid circuit for impedance matching circuit used in mobile communication apparatus, has adjustable impedance elements which are designed based on different technologies, different physical effects and different action principles - Google Patents

Abstract

The hybrid circuit (H) has adjustable impedance elements e.g. varactor whose impedance is adjusted by respective inner control signals. The adjustable impedance elements are designed based on different technologies, different physical effects and different action principles. The inner control signals provided to respective adjustable impedance elements, are different from one another.

Description

The invention relates to hybrid circuits whose impedance, for example their capacity, is adjustable.

Corresponding hybrid circuits may comprise impedance elements of different construction or impedance principles based on different functional principles and be connected, for example, in front-end circuits.

Adjustable impedance circuits may find use in impedance matching networks of mobile communication devices. For this they can be interconnected in the signal path of the device. By having its impedance adjustable, an impedance match between a variable impedance antenna and the antenna of subsequent circuits is achievable.

From the WO 2009/108391 A1 are DTCs (Digitally Tunable Capacitors = Digitally Tunable Capacitors) known. Such banks comprise a plurality of capacitive elements whose respective capacitance corresponds to a power of two 2 ⁿ * C _{0 of} a smallest capacitance Co. By means of semiconductor switches, the individual capacitive elements can be added individually to the capacity bank. Such a digitally tuned capacity bank is thus an example of a variable capacitance circuit element.

From the US 2008/0253057 A1 By way of example, MEMS capacitors, ie MEMS elements with adjustable capacitance, are known. Such switchable MEMS capacitors generally comprise two electrode layers arranged in parallel one above the other, one of the electrodes being fixed to a flexible element and the spacing of the electrodes being adjustable via a bias voltage applied to the electrodes. As a result of the adjustable spacing of the electrodes, the capacitance of the MEMS capacitor can also be adjusted.

Tunable capacity banks require a variety of switches to individually connect the capacitive elements. Furthermore, one independent signal line is required per switch for controlling the switch. In general, semiconductor switches are used which require control voltages of a few volts.

In contrast, MEMS elements require a bias voltage applied to the electrodes, with a so-called "closing voltage" being on the order of about 50 volts. Conventional mobile communication devices generally do not have a voltage source that can provide such a high voltage. Therefore, when using MEMS capacitors then so-called high voltage sources, eg. As charge pumps (charge pump), are provided to operate MEMS capacitors can.

It is an object of the present invention to provide an adjustable impedance circuit which meets high circuit linearity, switching speed, very finely adjustable impedance, simple and uncomplicated design requirements, or which utilizes adjustable impedance elements of different types ,

This object is achieved by a circuit according to claim 1. Dependent claims indicate embodiments of the invention.

• – „Beide Elemente beruhen auf unterschiedlicher Technologie”,
• – „Beide Elemente beruhen auf unterschiedlichen physikalischen Effekten”,
• – „Beide Elemente weisen unterschiedliche Wirkungsprinzipien auf”,
• – „Beide Elemente benötigen unterschiedliche innere Steuersignale zur Einstellung der Impedanz”.

The invention relates to a hybrid circuit, which comprises a first element of adjustable impedance whose impedance is adjustable by a first internal control signal. The hybrid circuit further comprises a second element of adjustable impedance whose impedance is adjustable by a second internal control signal. For the first or the second element of adjustable impedance, at least one of the following statements applies:

• - "Both elements are based on different technology",
• - "Both elements are based on different physical effects",
• - "Both elements have different principles of operation",
• - "Both elements require different internal control signals to adjust the impedance".

An inner control signal is a signal to be applied to an adjustable impedance element with which the impedance is controlled directly.

It has been recognized that the above object can be achieved with a hybrid circuit. A hybrid circuit according to the invention thus comprises adjustable impedance elements of different types. The advantages of such a hybrid circuit can be outweighed by the fact that different technologies of the impedance elements have to be used and that thereby an increased circuit complexity is obtained.

For example, while semiconductor switches generate circuits such as DTCs intermodulation products in RF circuits, MEMS capacitors have relatively high linearity in RF circuits. By contrast, DTCs have very high switching speeds.

As an element of adjustable impedance and varactors in the hybrid circuit can be used. Varactors provide infinitely variable capacitance within a certain capacity range. By applying a bias voltage, the adjustable capacitance is very finely adjustable.

In one embodiment, the hybrid circuit includes a first signal converter that converts an external control signal for adjusting the impedance of the first element into a first internal control signal.

An external control signal is a signal that can be provided by an external circuit and that has the information to control the impedance of the adjustable impedance element. For example, an n-bit signal simultaneously transmitted in n signal lines may simultaneously be an external and an internal signal. For example, an 8-bit signal designed for an 8-bit DTC is generally not an internal control signal for a MEMS capacitor because the voltage sufficient for operating semiconductor switches is too low for operating MEMS capacitors.

Thus, different technology based impedance elements generally require different internal control signals to adjust their impedance. However, if one interconnects one of the impedance elements with a signal converter, then both impedance elements can be driven in the same way. A first external signal can be converted by the signal converter into a first internal control signal. A second external control signal can act directly on the second impedance element.

The advantage of this is that a control circuit only has to have a single bus system in order, on the one hand, to address the second impedance element and, on the other hand, the combination of the first impedance element and the signal converter. The control bus can be executed digital or analog. The control bus can be a parallel bus in which different-value control signals can be transmitted at the same time, or a serial bus in which different-value control signals can be transmitted one after the other. The signal converter may include a high voltage source to activate, for example, MEMS capacitors.

In one embodiment, external control signals adjust the impedances of the first and second elements by means of at least one signal converter.

External control signals may originate, for example, from a logic circuit of a mobile communication device. The outer control signals can be tuned to a type of elements of variable impedance. Since the other variable impedance element requires a different type of control signal, only a single signal converter is needed to drive both elements.

But it can also be provided a second signal converter. In a corresponding embodiment, the hybrid circuit thus further comprises a second signal converter, which converts an external control signal for adjusting the impedance of the second element into a second internal control signal.

Thus, a logic circuit need not have a control signal output designed for control signals of one type of the impedance elements. Rather, logic circuits can be used with any conventional standard signal outputs. Similarly, corresponding standard bus systems can be used to transmit control signals to the impedance elements. The signal transducers can be arranged in the vicinity of the impedance elements. Then, a corresponding circuit may be equipped with a conventional bus system whose signal lines are executed by a logic circuit to almost the impedance elements in conventional design.

In one embodiment, the first signal converter comprises a digital-to-analog converter (D / A converter), an analog-to-digital converter (A / D converter) a voltage source such. B. a high voltage source for MEMS or a serial-to-parallel converter.

A digital-to-analog converter in the signal converter can be advantageous if, for example, a varactor is to be controlled. A serial or parallel transmitted digital signal is thereby converted by the digital-to-analog converter into a voltage with which the varactor is occupied. A voltage source may have a voltage which differs from a conventional operating voltage, for. B. provide for a MEMS capacitor or for a varactor. Parallel-to-serial converters or serial-to-parallel converters can convert digital or analog signals which are simultaneously available on parallel lines into a serial control signal. Analogously, serial-to-parallel converters can convert an in-provided serial signal into a parallel signal. Tunable capacity banks, for example, generally require a parallel control signal.

From the US 2006/0050350 A1 Arrays of MEMS capacitors are known. Each of the MEMS capacitors has a hysteresis curve, which determines the opening voltage (release voltage) and the closing voltage (closing voltage) of the respective MEMS element. The hysteresis curves can be nested one inside the other so that all possible 2 ⁿ circuit states of the corresponding capacitive element of the corresponding element of variable capacitance can be set with a time-variable control voltage. A signal converter according to the invention can provide the necessary time-variable control voltage as a serial signal.

In one embodiment, the first element and the second element are each adjustable capacitance elements. As adjustable capacitance elements, they can be used in impedance matching circuits.

Such variable capacitance elements may be connected to constant inductance inductive elements or capacitive elements of constant capacitance to cover an impedance range in the Smith Chart for impedance matching.

In one embodiment, the first element and the second element are each selected from an adjustable capacitor bank, for example, a digitally adjustable capacitor bank, a varactor, a capacitive element comprising MEMS capacitors, and a BST-comprising diode.

In one embodiment, the hybrid circuit is connected in a signal path of an impedance matching circuit of a mobile communication device.

In one embodiment, the first element is a capacitive element comprising MEMS capacitors and connected in series in the signal path, for example that of a mobile communication device. The second element is an adjustable capacitor bank and connects the signal path to ground.

Variable capacitance elements with MEMS capacitors have a particularly high linearity. It has been found that the requirements for linearity in capacitive elements connected in series in the signal path should be particularly high. By contrast, the requirements of linear capacitance connected in parallel paths between the signal path and ground capacitive element rather low. Here, a high number of achievable switching states and a high switching speed are required. MEMS components have a high linearity; rather semiconductor switches switched capacitor banks have a high switching speed and with 2 ⁿ possible switching states at sufficiently high n a high number of achievable switching states.

Only the use of hybrid circuits with different types of impedance elements allows for a customized variable impedance circuit that is optimized for requirements such as linearity or switching speed. This advantage outweighs the corresponding disadvantages of high switching costs and possibly high costs.

In an embodiment, the hybrid circuit comprises a control bus connected to the first element and to the second element. In the control bus external control signals for adjusting the impedance of the first element and the second element are transferable.

As already indicated above, it is quite possible to transmit external control signals which are at the same time internal control signals for at least some of the impedance elements. Then it is only necessary to provide at most n-1 signal transducers for n different types of impedance elements.

In one embodiment, the control bus is a conventional control bus. An I ² C bus, a Serial Peripheral Interface (SPI) bus, an RF bus, a MIPI bus and an I ₂ S bus are all possible.

The hybrid circuit will be explained in more detail below on the basis of exemplary embodiments and associated schematic figures.

Show it:

1 a basic form of the hybrid circuit with impedance elements of adjustable impedance,

2 an embodiment with adjustable capacitive elements, which are connected to a signal path of a mobile communication device,

3 an embodiment with two signal transducers,

4A schematically a capacitor bank,

4B a varactor diode,

4C the basic principle of a MEMS capacitor,

5 the information flow of a logic circuit via a bus system to impedance elements of variable impedance.

1 shows a hybrid circuit H having a first variable impedance element E1 and a second variable impedance element E2. A first inner control signal IS1 is transmitted to the first element of variable impedance E2. A second internal control signal IS2 is transmitted to the second element of variable impedance E2. The control signals IS1, IS2 control the impedance of the elements of adjustable impedance E1, E2. The elements of adjustable impedance E1, E2 are of different types and require different types of internal control signals IS1, IS2. The provision of these internal control signals IS1, IS2 can be done by an external circuit. The provision of different types of internal control signals means an increased circuit complexity of the corresponding circuit, which provides the internal control signals. However, in the design of hybrid circuit H, the different advantages of different types of variable impedance elements E1, E2 can be taken into account and used.

2 shows an embodiment of the hybrid circuit H wherein elements of variable capacitance C1, C2 are provided as elements of variable impedance. External control signals AS1, AS2 are transmitted to the hybrid circuit H via a control bus SB. The first variable-capacitance element C1 comprises a first signal converter SW1, which converts the first external control signal AS1 into a first internal control signal IS1. The first inner control signal IS1 is matched to the technological requirements of the first variable capacitance element C1. In the in 2 In the embodiment shown, the second external signal AS2 already corresponds to the required second internal signal IS2, which sets the capacitance of the second variable capacitance element C2. Thus, no signal converter is necessary which converts the external control signal AS2 into an internal control signal IS1.

The first variable-capacitance element C1 is connected in series in a signal path SP. The second variable capacitance element C2 is connected in a parallel path between the signal path SP (PP) and ground.

Due to the higher linearity requirements in the signal path, the first variable capacitance element C1 is advantageously a capacitive element based on MEMS technology.

3 shows an embodiment of the hybrid circuit H which is part of an impedance matching circuit IAS of a mobile communication system (not shown). The difference of the hybrid circuit H of 3 to the hybrid circuit H of 2 consists in the second signal converter SW2, which in the hybrid circuit H of 3 is connected as part of the second variable capacitance element C2. The second signal converter SW2 converts a second external signal into a second internal signal IS2. The hybrid circuit H of 3 Thus, per element of variable capacitance C1, C2 exactly one signal converter SW1, SW2 which supplies the respective capacitive element of the variable capacitance element C1, C2 with an internal control signal IS1, IS2.

4A schematically shows the operation of a capacity bank. Four capacitive elements KE are connected in parallel with each other. In series with each capacitive element, a switch S is connected, with which the capacitive element can be connected to the capacity bank KB, to adjust the total capacity.

4B shows a varactor diode whose capacitance can be adjusted continuously by applying an external bias voltage (Bias Voltage).

4C schematically shows the operation of a MEMS capacitor MEMS. Such a capacitor comprises two electrodes EL wherein one of the electrodes is movably arranged so that the pitch of the electrodes EL can be adjusted. A dielectric D may be arranged between the electrodes EL in order to prevent short-circuiting of the electrodes EL upon activation, ie upon application of the closing voltage. Depending on the voltage applied to the electrodes EL of the MEMS capacitor, the movable electrode is used to different degrees to the opposite diode. The capacity of a plate capacitor from the distance of the electrodes of the electrodes. By adjusting a suitable electrode spacing, the capacitance of the MEMS capacitor can thus be adjusted. It is also possible to operate the MEMS capacitor digitally and to operate it either in an open or in a fully closed state.

5 illustrates the information flow of control signals from a logic circuit LS to the capacitive elements of different operation. The logic circuit LS assumes the task of generating the outer control signals. The logic circuit can be a digital or an analog circuit. In the case of a feedback loop between the impedance elements and the logic circuit, the logic circuit is a control circuit.

Suitable capacitive elements are MEMS capacitors, BST-based varactors, capacitance banks or varactors connected by means of CMOS, NMOS or GaAs switches. Control signals are transmitted from the logic circuit to the variable capacity elements via a common bus system. If necessary, the adjustable impedance elements comprise corresponding ones Signal converter, so that the capacitances of the capacitive elements of different types are set according to the similar bus control signals.

The individual advantages of the different technologies of adjustable impedance elements can be used. Furthermore, a developer remains essentially free in the selection of adjustable impedance elements because he does not have to adapt his bus system in a complicated way to all technologies of the impedance elements. Namely, the adaptation to a standard bus is accomplished within the variable impedance elements. A developer of an impedance matching circuit thus enjoys a higher degree of freedom and fewer restrictions in the selection of the impedance elements.

Furthermore, impedance elements of different functionality can be more easily replaced by impedance elements of a different design, both during planning and in a finished product.

The invention is not limited to the exemplary embodiments shown. Combinations or variations which, for example, comprise further impedance elements or control lines or any combinations thereof, likewise represent exemplary embodiments according to the invention.

LIST OF REFERENCE NUMBERS

• AS1, AS2

  first, second outer control signal

  C1, C2

  first, second variable impedance element

  D

  dielectric

  E1, E2

  first, second variable impedance element

  EL

  electrode

  H

  hybrid circuit

  IAS

  Impedance matching circuit

  IS1, IS2

  first, second inner control signal

  KB

  capacitance bank

  KE

  capacitive element

  LS

  logic circuit

  MEMS

  Micro-electro-mechanical system

  PP

  parallel path

  S

  switch

  SB

  control bus

  SP

  signal path

  SW1, SW2

  first, second signal converter

  V

  varactor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2009/108391 A1 [0004]
• US 2008/0253057 A1 [0005]
• US 2006/0050350 A1 [0025]

Claims (11)

Hybrid circuit comprising A first element of adjustable impedance whose impedance is adjustable by a first internal control signal A second element of adjustable impedance whose impedance is adjustable by a second internal control signal, wherein for the first and the second element of adjustable impedance at least one of the following statements applies: - both elements are based on different technology, - both elements are based on different physical effects, - both elements have different principles of action, - Both elements require different internal control signals to adjust the impedance. A hybrid circuit according to the preceding claim, further comprising a first signal converter which converts an external control signal for adjusting the impedance of the first element into a first internal control signal. A hybrid circuit according to the preceding claim, wherein external control signals adjust the impedances of the first and second elements by means of at least one signal converter. A hybrid circuit according to any one of the preceding claims, further comprising a second signal converter which converts an external control signal for adjusting the impedance of the second element into a second internal control signal. Hybrid circuit according to one of the preceding claims, wherein the first signal converter comprises a digital-to-analog converter, a voltage source, a parallel-serial converter or a serial-parallel converter. A hybrid circuit according to any one of the preceding claims, wherein the first element and the second element are adjustable capacitance elements. Hybrid circuit according to one of the preceding claims, wherein the first element and the second element are each selected from an adjustable capacitor bank, a varactor, a diode comprising BST and a capacitive element comprising MEMS capacitors. Hybrid circuit according to one of the preceding claims, wherein the hybrid circuit is connected in a signal path of an impedance matching circuit of a mobile communication device. Hybrid circuit according to the preceding claim, wherein The first element is a capacitive element comprising MEMS capacitors and is connected in series in the signal path, - The second element is an adjustable capacitor bank and connects the signal path to ground. Hybrid circuit according to one of the preceding claims, further comprising a control bus, - connected to the first element and to the second element, - In the outer control signals for adjusting the impedance of the first element and the second element are transferable. A hybrid circuit according to the preceding claim, wherein the control bus is selected from an I ² C bus, an SPI bus, a USB bus, an RF bus, a MIPI bus and an I ² S bus.

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