Patent Application
20050059371
The invention relates to a circuit array with a switch unit, which has an antenna input, a signal input and a signal output. In addition, the switch unit has a control line, which can be used optionally to control the transfer of a connection between the antenna input and the signal input or the signal output. The antenna input of the circuit array is connected to a protective device against electrostatic discharges.
Circuit arrays of the type mentioned above are often used as multi-band front-end modules for mobile telephones. In this application, they are connected to the antenna of a mobile telephone at the antenna input. When the antenna comes into contact with an electrically-charged user, this can result in electrostatic discharge, also known under the name “electrostatic discharge (ESD)”. These electrostatic discharges can create voltage peaks that are capable of destroying the circuit array. Thus, it is necessary to equip circuit arrays of the type mentioned above with a device that protects against ESD.
Printed specification WO 00/57515 discloses circuit arrays of the type mentioned above that are equipped with a protective device against ESD. The protective device comprises an electric high-pass filter in which a capacitor is connected in series and an inductor is connected in parallel to the antenna input path.
A drawback of the known circuit array is that the ESD protective device only helps reduce the ESD impulse entering the circuit array directly through the antenna.
In addition to the impulse entering the circuit array directly through the antenna, an electrostatic discharge can also generate a high voltage in the circuit array through ground coupling. This can occur, for example, because the control input normally used in a circuit is arranged either on a high voltage (high) or on a low voltage (low). In this case, the high voltage (high) is defined, for example, by the fact that it lies 2.3 V above the ground voltage of the circuit array. Because, in the case of a mobile telephone, as with many other devices based on signal transmission via antennas, the signal input runs from the antenna to the system's ground, an electrostatic discharge can also directly affect the ground voltage of the circuit array in a circuit array of the type mentioned above. As a result of the directly coupling of a control line to ground through the “high” condition, the voltage impulse resulting from an electrostatic discharge can not only affect the path, via the antenna, but also the circuit array, via the control line. The known circuit array is not protected against these effects.
In addition, the high-pass filter used in the known circuit array has the characteristic of being a very simply designed filter that allows all frequency components of a signal, beginning with a certain cutoff frequency, to pass through it virtually unimpeded. In general, however, only a very narrow frequency range is relevant to the further processing of the signal received by the antenna in a mobile telephone. For example, frequencies between 1 and 2 GHz are used in mobile telephones based on the GSM, PCN or PCS standard. All other frequencies received by the antenna tend to be interfering and, therefore, must be filtered out. Accordingly, at least one band-pass filter is needed to make the signal captured by the circuit array mentioned above capable of being processed for a mobile telephone.
The high-pass filter arranged in the known circuit array can only cut off frequencies below a certain cutoff frequency. For this reason, at least one filter circuit must be connected downstream from this filter, in order to remove the frequency range relevant to the mobile telephone from the signals received by the antenna.
Accordingly, an advantage of the known circuit array is that the high-pass filter circuit used to protect against ESD has an insertion loss, causing the wanted signals to undergo a certain attenuation, although cutting of the transmitted frequency band does not take place. Accordingly, a disadvantage of the known circuit array, operating in conjunction with the filtration, which is also needed, is a generally high insertion loss.
The goal of this invention, therefore, is to provide a circuit array of the type mentioned above, in which the protective device against electrostatic discharges has a low insertion loss.
This goal is achieved through a circuit array according to claim 1. Additional advantageous embodiments of the invention, as well as a circuit module and the use of the circuit module can be seen from the dependent claims.
A circuit array is described that contains a switch unit with an antenna input, a signal input, and a signal output. The switch unit is suitable for electrically connecting the antenna input with either the signal input or the signal output. Additionally, the antenna input is connected to a first protective device against electrostatic discharges.
The first protective device against electrostatic discharges has an antenna input and a switch output, wherein the switch output is connected to the antenna input of the switch unit. The antenna input of the protective device and the switch output of the protective device are connected to a line. A voltage-limiting element, which can be a varistor, a spark gap or a charge eliminator, is connected in parallel to ground. The voltage-limiting element is connected to a ground.
With the aid of the voltage-limiting element, excess voltage applied to the antenna input of the protective device can be discharged to ground. This means that the key function of the protective device consists of limiting the voltage applied to the antenna input of the switch unit.
An advantage of the circuit array of the invention is that, as a result of the special design of the protective device, a filter function is omitted, which results in a low insertion loss in the first protective device.
However, the protective mechanism of the circuit array can be improved by connecting an inductor in parallel to the voltage-limiting element. The inductor is in turn connected to the ground. The inductor connected in parallel to the voltage-limiting element is suitable for discharging very low frequencies to ground. Thus, as a result of the protective device, high frequencies are transmitted from the antenna input to the switch unit without being modified.
It is also advantageous if a first inductor is connected between the antenna input and the voltage-limiting element and a second inductor between the voltage-limiting element and the switch output, both being connected in series to the line. As a result of these two additional inductors, the impedance of the protective device can be adjusted to conform to the normal value for high-frequency ranges, 50 Ω.
In particular, a low insertion loss in the first protective device of <0.3 dB can be achieved though suitable selection of the inductances between 0 and 47 nH.
In addition, a control line that controls the switch position of the switch unit can be arranged in the switch unit.
In addition, protection against excess voltage (ESD protection) can be further improved by also connecting the control line of the circuit array with a second protective device against electrostatic discharges. As a result, the excess voltage input into the switch unit through ground couplings and applied to the control line can be reduced in an especially effective manner.
The protective devices against electrostatic discharges are advantageously connected to a ground connection, into which the excess voltage from the electrostatic discharges can be discharged.
The switch unit can, for example, be a voltage-controlled switch, such as the type normally used in mobile telephone because of its low power consumption. In particular, a gallium-arsenide switch can be used as the switch unit.
The switch unit can also have multiple signal inputs and outputs. Accordingly, multiple control lines are needed.
The gallium-arsenide switch can also be provided with a decoder, which can be used to reduce the number of control lines. Such a decoder normally requires a power supply, which is connected via a supply line. The ESD protection of such a circuit can be improved even further by connecting the supply line to a third protective device against electrostatic discharges.
In addition, a circuit module is specified that contains a circuit array according to the invention. The circuit module also contains a multilayer ceramic substrate with integrated passive components, which form electric frequency filters. These frequency filters are assigned to the signal inputs or outputs. The switch unit, which can be implemented with the aid of PIN diodes or in the form of a gallium-arsenide switch, for example, is arranged on the upper side of the multilayer ceramic substrate. Furthermore, the first and second protective devices against electrostatic discharges are integrated into the circuit module.
The circuit array can also contain frequency filters that are assigned to individual signal inputs or signal outputs. They are especially suitable for filtering the frequencies received by the antenna on a mobile telephone in such a way that the signals conducted and filtered through the signal output can be processed further by the mobile telephone. The same applies to the signal inputs of the circuit array, which, in a mobile telephone, are used to transmit the voice signals generated in the mobile telephone to a receiver via the antenna.
The use of a varistor, which is connected in parallel to the control line and is also connected to the ground potential, represents another option that can be considered for a second protective device against electrostatic discharges. Such a varistor has a very low resistance beginning at a certain cutoff voltage, so that excess voltage can be diverted to ground. Varistors with low switching voltage are especially suitable, because in this case the residual voltage that occurs in a voltage impulse and loads the circuit array is lowest. For this reason, it is advisable to use varistors with a varistor voltage of between 4 and 20 V. Accordingly, the terminal voltage in a voltage impulse that loads the circuit array is about 8 to about 50 V. As a result, the circuit array can be reliably protected against destruction in the event of an ESD impulse.
Another possibility is to use a switch spark gap or a Z-diode as a second protective device against electrostatic discharges.
The invention also specifies a circuit array in which the antenna input is connected to an antenna, in which the signal output is connected to a receiving amplifier of a mobile telephone, and in which the signal input is connected to a transmission amplifier of a mobile telephone.
In addition, a circuit module is specified which contains a circuit array according to the invention. The circuit module also contains a multilayer ceramic substrate with integrated passive components, which form electric frequency filters. These frequency filters are assigned to the signal inputs or outputs. The switch unit, which can, for example, be implemented with the aid of PIN diodes or in the form of a gallium-arsenide switch, is arranged on the upper side of the multilayer ceramic substrate. In addition, the first and, if applicable, second protective device against electrostatic discharges is integrated into the circuit module.
An advantage of the circuit module is that, as a result of the integration of the passive components into the ceramic substrate, as well as the integration of the protective device into the circuit module, a high degree of integration is achieved, which advantageously affects the space requirements of the circuit module. The integration of the first and, if applicable, second protective device into the circuit module can occur, for example, by mounting these components onto the surface of the ceramic substrate, adjacent to the switch unit.
In particular, it is also advantageous to use the circuit module as a front-end module in a mobile telephone.
In the following, the invention is explained in greater detail on the basis of example embodiments and the corresponding diagrams.
The same reference symbols refer to the same elements in all diagrams.
The first protective device 6 has an antenna input 111 and a switch output 112. The antenna input 111 and the switch output 112 are connected to one another by a line 1113. Two inductors L1 and L2 are connected in series to the line 1113. These two inductors L1 and L2 serve to adjust the impedance to a value of 50 Ω. Between the two inductors L1 and L2, another inductor L3 and a voltage-limiting element 114 branch off in a parallel circuit to the line 113. The voltage-limiting element 114 can be a varistor, for example. The inductor L3, as well as the varistor, are connected to the ground 8 of the circuit array. The varistor limits the voltage input into the switch unit 4. The switching voltage of the varistor, which should be between 4 and 8 V, is especially important at this point. The smaller the switching voltage of the varistor, the more effectively can excess voltage be diverted and therefore suppressed with regard to the switch unit 4. A varistor switching voltage of 6 V or less is advantageous. This also applies to the second and third protective device 7, 12. The switching voltage of the varistor is the residual voltage that remains from the high-voltage impulse and is conducted through the protective device to the switch unit 4.
The inductances in the first protective device preferably have the following values:
In particular, an insertion loss in the first protective device less than 0.3 dB can be achieved through suitable selection of the inductances (L1=1 nH, L2=1 nH, L3=47 nH).
The control inputs E1, E2, and E3 of the decoder 10 are connected to the control lines 5.
An example of the decoding of a logical signal applied to one of the inputs E1, E2, and E3 of the decoder 10 into signals applied to the control inputs S1, S2, S3, S4, and S5 of the GaAs switch 9 that are suitable for controlling the GaAs switch is described by the following translation table:
In this case, the transmitter inputs TX1 and TX2 correspond to the signal inputs from
The signal inputs 2 of the GaAs switch 9 are electrically connected to transmitter amplifiers 19. The transmitter amplifiers 19, like the low-pass filters 13, 14, are adjusted to radio frequencies GSM and PCN/PCS, respectively. The signal outputs are electrically connected to receiver amplifiers 19a through the band-pass filters 15, 16, 17, wherein the receiver amplifiers 19a are adjusted to the frequency bands GSM, PCN and PCS, respectively. The antenna input 1 of the GaAs switch 9 is connected to an antenna 18. The signals received by the antenna 18 can now be fed, by means of the GaAs switch 9, into the band-pass filter 16, the band-pass filter 17 or the band-pass filter 18, where they are filtered according to the radio frequency used and further processed in amplifiers 19a. The signals supplied by the transmitter amplifiers 19 are filtered by the low-pass filters 13, 14 and optionally supplied to the antenna 18 for transmission of a signal.
The switch unit 4 can, for example, be secured and electrically contacted by means of gluing and additional wire-bonding. A GaAs multiple switch is preferably used as the switch unit 4. This type of switch can have an insertion loss of 0.8 dB in the frequency range between 1 and 2 GHz. It can be an integrated circuit with FET produced on a gallium-arsenide base, with its pin surfaces connected to the ceramic substrate 20 by soldering.
The switch unit 4 can also be attached to the multilayer ceramic substrate 20 and electrically bonded by means of wire bonding. Bonding by means of soldering is preferred when the switch unit 4 is to be used with an additional housing.
The passive components 21, 22, 23 can form the filters 13, 14, 15, 16, 17 required in accordance with
In addition to the switch unit 4, the first protective device 6 and the second protective device 7 are also mounted onto the surface of the substrate 20. This accomplishes a high degree of integration for the circuit module according to the invention, which advantageously affects the space requirements of the circuit module.
Such a circuit module can be used in mobile telephones, for example, and it is for this reason that the advantageous use of the circuit module of the invention as a front-end module in a mobile radio device is also the subject matter of the invention.
The invention is not limited to the examples of the second and third protective device mentioned above; instead, all conceivable protective devices can be used in the circuit array of the invention. In addition, the circuit array or the circuit module is not limited to applications in mobile telephones.
| Number | Date | Country | Kind |
|---|---|---|---|
| 101 47 985.9 | Sep 2001 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE02/03687 | 9/30/2002 | WO |
