WO2016010466A1

WO2016010466A1 - A limiter module and a transceiver for reducing leakage of a transmitted signal

Info

Publication number: WO2016010466A1
Application number: PCT/SE2014/050897
Authority: WO
Inventors: Bo Zhou; Jian Liu; Carlos GU
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-07-16
Filing date: 2014-07-16
Publication date: 2016-01-21

Abstract

A limiter module adapted for use in a transceiver and adapted for reducing leakage of a transmitted signal is provided. The limiter module (140) comprises two channels, wherein each channel comprises at least two diodes (144a, 147a, 144b, 147b), a first diode (144a, 144b) and a second diode (147a, 147b), connected in parallel to each other along a transmission line (142a, 142b) between an input (141a, 141b) and an output (141a, 141bb) of the channel. Each channel further comprises one capacitance (146a, 146b) arranged in the transmission line between the two diodes. The transmission line (142a, 142b) is arranged with a connection (148a, 148b) to ground between the second diode (147a, 147b) and the output of the channel (141aa, 141bb), and with a connection (145a, 145b) to an exposed pad between the first diode (144a, 144b) and the capacitance (146a, 146b).

Description

A LIMITER MODULE AND A TRANSCEIVER FOR REDUCING LEAKAGE OF A

TRANSMITTED SIGNAL

Technical field

[0001 ] The present disclosure relates to a limiter module for use in a transceiver and adapted for reducing leakage of a transmitted a signal.

Background

[0002] In frequency division, FD, systems, because of the separated signal channels provided by the duplexer, receiver circuit can hardly be damaged by transmitted signals. In time division, TD, systems, transmitted and received signals work at the same frequency. It is important to provide receiver front circuit protection. When transmission is on, transmission power has high risk of leakage to receiver channels. The receiver circuit may be quite sensitive and it may be easily damaged by the leakage power.

[0003] Receiver protection e.g. in modern radars, is playing an increasingly vital role in order to meet the challenges of interference threats and

electromagnetic environments. Limiter circuits are widely used in military Radar for its extreme high transmission power. When the input power level is low, the electrical impedance of a limiter diode is determined by the capacity of the diode structure. When the power level is high, the impedance is determined by the sum of the electrical resistances in the highly doped regions of the diode structure in the contacts. Depending on the diode driven application, there are 3 categories: passive limiters, active limiters, and self-biased limiters. Passive limiter: Limiting of all incident in-band radio frequency, RF, pulses without power supplies. Active limiter is triggered by a system command (Transistor-Transistor-Logic, TTL level, for example). Self-biased limiter is driven by a detector in the limiter module.

[0004] Solid-state receiver protection techniques have been deployed across a wide range of conventional and phased-array radar system architectures, providing low-loss protection elements that are capable of withstanding high incident powers from local and remote radar transmitters, along with other Electro Magnetic Compatibility, EMC, threats. Diode, packaging and detector- drive schemes are factors considered in limiter protector design.

[0005] Limiter receiver protection developed in planar circuits; need to be integrated in receiver circuit board architectures to provide low-loss protection elements. The integration of further system functionality within the receiver protector assembly supports a further optimisation of the system receiver chain, while providing an overall reduction in the system mass, size and cost.

[0006] With active protectors, a synchronous control signal is needed. With the bias circuit, very high isolation is provided and RF path to the receiver is blocked. But if the synchronous control signal has time alignment problem or Radio Unit, RU, meets unexpected interference signal from outside (complex

electromagnetic, EM, environment on site), receiving front LNA would be destroyed.

[0007] For passive limiter modules, leakage power to the LNA may be larger than for the active limiter module. Some LNA modules can't stand continuous input power less than 15dBm. Multiple limiter diodes cascaded together may improve that but would increase insertion loss.

[0008] A self-biased limiter may have similar isolation like active limiter but may be boosted by the additional bias current sourced from inside coupler. The inside coupler will increase module size. With built-in coupler, the module can't work on wide frequency band and extra cost is required to use the limiter in other frequency bands. The self-biased limiter provides auto protection like passive limiter, but not controllable. So it may not be able to fulfil TD communication system requirements and some extra function blocks are needed, e.g. bypass function, etc.

Summary

[0009] The object is to obviate at least some of the problems outlined above. In particular, it is an object to provide a limiter module adapted for use in a

transceiver and adapted for reducing leakage of a transmitted signal. It is a further object to provide a transceiver comprising such a limiter module. These objects and others may be obtained by providing a limiter module and a transceiver according to the independent claims attached below.

[00010] According to an aspect a limiter module adapted for use in a transceiver and adapted for reducing leakage of a transmitted signal is provided. The limiter module comprises at least two channels, wherein each channel comprises at least two diodes, a first diode and a second diode, connected in parallel to each other along a transmission line between an input and an output of the channel. Each channel further comprises one capacitance arranged in the transmission line between the two diodes. The transmission line is arranged with a connection to ground between the second diode and the output of the channel, and with a connection to an exposed pad between the first diode and the capacitance.

[0001 1 ] According to an aspect, a transceiver comprising such a limiter module is also provided.

[00012] The limiter module and the transceiver may have several possible advantages. One possible advantage is that the limiter module may be more reliable than a transmission-reception switch under unexpected interference.

Another possible advantage is that this balanced limiter module may have better radio link performance and half the input power. By "balanced" means that the input signal is divided by a coupler into two signal channels. These two channels are called balanced. The heat sink may be better and the total parasitic effects may be decreased. The limiter module may increase flexibility of the transceiver without requiring bias control and driven circuits, which in turn may reduce cost. With bias control, the limiter module may operate as a switch, wherein receiving signal path may be selected according to different function needs.

Brief description of drawings

[00013] Embodiments will now be described in more detail in relation to the accompanying drawings, in which: [00014] Figure 1 a is a block diagram of a transceiver comprising a limiter module according to an exemplifying embodiment.

[00015] Figure 1 b is a block diagram of a limiter module according to an exemplifying embodiment.

[00016] Figure 1 c is a block diagram of a limiter module according to an exemplifying embodiment.

[00017] Figure 1 d is a block diagram of a limiter module according to yet an exemplifying embodiment.

[00018] Figure 2 is an exemplifying illustration of an envelope the limiter module of figures 1 b, 1 c and 1 d.

[00019] Figure 3 is an exemplifying illustration of the limiter module with low radio frequency power.

[00020] Figure 4 is an exemplifying illustration of the limiter module with high radio frequency power.

[00021 ] Figure 5 is an exemplifying illustration of a circuit matched with different frequencies.

[00022] Figure 6 illustrates graphs of protector circuit S-parameters when the input power level for B39 (1.88GHz-1 .92GHz) is low.

[00023] Figure 7 illustrates graphs of protector circuit S-parameters when the input power level for B39 is high.

[00024] Figure 8 illustrates graphs of protector circuit S-parameters when the input power level for B41 (2.48GHz-2.7GHz) is low.

[00025] Figure 9 is illustrates graphs of protector circuit S-parameters when the input power level for B41 is high. Detailed description

[00026] Briefly described, a Iimiter module adapted for use in a transceiver and adapted for reducing leakage of a transmitted signal is provided. Further, a transceiver comprising the Iimiter module is provided. The Iimiter module comprises both diodes and a capacitance (or a capacitor) as well as a couple of connections to either ground or an exposed pad along a transmission line from an input of a channel of the Iimiter module to an output of the Iimiter module.

Together, the diodes, the capacitance and the connections to either ground or an exposed pad attenuate any possible leakage from a transmitted signal of the transceiver in order to protect e.g. a Low Noise Amplifier of the transceiver.

[00027] Exemplifying embodiments of such a Iimiter module will now be described with reference to figures 1 a-1 d.

[00028] Figure 1a is a block diagram schematically illustrating a transceiver 100 comprising a Iimiter module 140.

[00029] Figure 1 b illustrates the Iimiter module 140 adapted for use in a transceiver and adapted for reducing leakage of a transmitted signal, the Iimiter module 140 comprising at least two channels, wherein each channel comprises at least two diodes 144a, 147a, 144b, 147b, a first diode 144a, 144b and a second diode 147a, 147b, connected in parallel to each other along a transmission line 142a, 142b between an input 141 a, 141 b and an output 141 a, 141 bb of the channel. Each channel further comprises one capacitance 146a, 146b arranged in the transmission line between the two diodes. The transmission line 142a, 142b is arranged with a connection 148a, 148b to ground between the second diode 147a, 147b and the output of the channel 141 aa, 141 bb, and with a connection 145a, 145b to an exposed pad between the first diode 144a, 144b and the

capacitance146a, 146b.

[00030] The Iimiter module may be incorporated into a transceiver, wherein the Iimiter module reduces leakage of the transmitted signal into a receiving part of the transmitter, the transmitted signal being transmitted from a transmitting part of the transceiver to another device, or receiver. [00031 ] Figure 1 a, illustrates that a signal may be received by means of an antenna 1 10 which then first passes a circulator 120. The circulator has three connections, a first to the antenna 1 10, a second to a coupler 130, and a third to a transmitting part, or power amplifier, PA, 180. The circulator operates in such a manner that a signal being received on the third connection, i.e. from the PA 180 is outputted on the first connection, i.e. forwarded to the antenna 1 10. A signal being received on the first connection, i.e. from the antenna 1 10, is outputted on the second connection, i.e. forwarded to the coupler 130. However, the circulator 120 is not perfect and thus parts of the signal transmitted from the PA 180 leak to the second connection and are thus outputted towards the coupler 130. In order to protect components of the receiving parts of the transceiver 100, e.g. a Low Noise Amplifier, LNA 150, the limiter module 140 is arranged in a path between the circulator 120 and the LNA 150.

[00032] The limiter module 140 comprises two channels. Each channel comprises at least two diodes 144a, 147a, 144b, 147b, the first diode 144a, 144b and the second diode 147a, 147b, connected in parallel to each other along a transmission line 142a, 142b between an input 141 a, 141 b and an output 141 aa, 141 bb of the channel. Thus leakage from the transmitted signal, received by means of the input 141 a, 141 b of the limiter module, i.e. the channel, may by weakened by the first diode 144a, 144b as parts of the leaked signal will go through the first diode 144a, 144b and then to ground, and only the remaining part will travel along the transmission line 142a, 142b towards the second diode 147a, 147b.

[00033] In the same manner, parts of the remaining weakened part of the leaked signal will pass through the second diode 147a, 147b, and then to ground and only a part of the already weakened signal will continue travelling along he

transmission line 142a, 142b towards the output 141 aa, 141 bb of the channel. Thus the leaked signal will be weakened twice travelling along the transmission line 142a, 142b between the input 141 a, 141 b and the output 141 aa, 141 bb of the channel. The second diode 147a, 147b can stand less power and have much smaller power leakage compared with the first diode 144a, 144b. [00034] The first diode 144a, 144b may be chosen such that the first diode 144a, 144b is able to stand high power signals but the leakage may be large without a bias circuit. The bias circuit, also referred to as a driven circuit, will be explained in more detail below. The second diode 147a, 147b may be chosen such that second diode 147a, 147b is able to cover, or attenuate, the leakage from the first diode 144a, 144b, but the second diode 147a, 147b can't stand high power signals.

[00035] Further, each channel comprises one capacitance 146a, 146b arranged in the transmission line between the two diodes. As the first diode 144a, 144b may be used in an active way when the exposed pad is connected to a driven circuit (as will be explain in more detail below, there may be a need to block direct current, DC. The capacitance 146a and 146b may block a DC signal.

[00036] When the input power level is low, i.e. the power level of the signal, the electrical impedance of a diode may be determined by the junction capacity of the diode. Figure 3 illustrates an example of the equivalent circuit of the module when the input power level is low.

[00037] When the input power level is high, i.e. the power level of the leakage of the transmitted signal, the diode is nearly short circuit to ground. Figure 4 is the equivalent circuit of the module when input power is high. Switch time between 2 modes (e.g. between the modes illustrated in figures 3 and 4) may be less than 100ns.

[00038] Figures 3 and 4 are schematic simulations of RF performance for the limiter module 140.

[00039] In figure 3, the capacitances 143a, 146a and 149a are indicated as "chip capacitance". The corresponding capacitances 143b, 146b and 149b are also illustrated in the "lower" channel even though the denotations are not present in the figure. Likewise, the first diode 144a, 144b and the second diode 147a, 147b are illustrated as capacitances and indicated as "Limiter Equivalence" in figure 3. When the input power level of a signal, e.g. the leaked signal, is low, the first and second diodes 144a, 144b, 147a, 147b act as capacitors or capacitance. [00040] In figure 4, the capacitances are illustrated, however lacking denotations in order to not clutter the figure. The first and second diodes 144a, 144b, 147a, 147b are illustrated as resistors or resistance. This is because, when the input power level of a signal, e.g. the leaked signal, is high, the first and second diodes 144a, 144b, 147a, 147b act as resistors or resistance.

[00041 ] The limiter module further comprises the connection 145a, 145b to an exposed pad arranged at the transmission line 142a, 142b between the first diode 144a, 144b and the capacitance 146a, 146b. The exposed pad may be either connected to ground or connected to a driven circuit. When the exposed pad is connected to ground and not to the driven circuit, a control circuit may be omitted, but the limiter module 140 can't stand as much power as if the exposed pad is connected to driven circuit. The power level that the limiter module may be able to stand may be calculated by the parameters from a diode datasheet. The limiter module 140 may thus be used for different requirement by means of the driven circuit connected to the exposed pad of connection 145a, 145b.

[00042] The limiter module 140 further comprises the connection 148a, 148b to ground arranged at the transmission line 142a, 142b between the second diode 147a, 147b and the output of the channel 141 aa, 141 bb. As for the connection 145a, 145b, part of the leaked signal travelling along the transmission line 142a, 142b will come to the connection 148a, 148b to ground. By the connection to ground, the second diode 147a, 147b becomes as passive limiting component as compared to the first diode 144a, 144b when the connection 145a, 145b is connected to the driven circuit via the exposed pad making the first diode 144a, 144b an active limiting component. The second diode 147a, 147b and the connection 148a, 148b to ground provide protection for the receiver.

[00043] Each of the at least two diodes 144a, 147a, 144b, 147b, the capacitance 146a, 146b, and the connections 145a, 145b, 148a, 148b may be seen as attenuation stages, where the leakage of the transmitted signal is attenuated so that the possible remaining part of the leakage of the transmitted signal, i.e. the leaked signal, is small enough to not cause any damage to other components or circuitries, e.g. the LNA 150, of a transceiver 100 in which the limiter module 140 may be arranged or comprised.

[00044] The limiter module may have several possible advantages. One possible advantage is that the limiter module may be more reliable than a transmission- reception switch under unexpected interference. Another possible advantage is that this balanced limiter module may have better radio link performance and half the input power. By "balanced" means that the input signal is divided by coupler 130 into two signal channels. These two channels are called balanced. The heat sink may be better and the total parasitic effects may be decreased. The limiter module may increase flexibility of the transceiver without requiring bias control and driven circuits, which in turn may reduce cost. With bias control, the limiter module may operate as a switch, wherein receiving signal path may be selected according to different function needs.

[00045] According to an embodiment, the connection to ground 148a, 148b between the second diode and the output of the channel is provided with an inductance 148aa, 148bb.

[00046] An inductor, i.e. a coil, is a passive two-terminal electrical component which resists changes in electric current passing through it. This will provide protection for the receiver, 150. The inductance provides a DC short to ground and isolates the radio frequency signal. According to yet an embodiment, the

connection 145a, 145b to the exposed pad between the first diode and the capacitance is provided with an inductance 145aa, 145bb.

[00047] The first diode 144a, 144b may be described as an incident power controlled, radio frequency variable resistor. When the power of an input signal is low, the impedance of the first diode 144a, 144b is at its maximum (only very small capacitance left), which produces minimum insertion loss, typically less than 0.1 dB. When the power of an input signal is high input signal, it forces the impedance of the first diode 144a, 144b to a much lower value, which produces an impedance mismatch, which reflects the majority of the input signal power back towards its source. [00048] During the limiting process, i.e. when there is a leaked signal coming to the limiter module, a DC current is generated by the first diode 144a, 144b. The current is produced by charge carriers being forced into an Ί" layer of the diode by forward alternations (like sine wave) of the high power input radio frequency signal. A complete path should be provided for this current or the diode is not capable of limiting. Therefore, the connection 145a, 145b may be provided by the inductance 145aa, 145bb to complete the path for DC current flow. When the exposed pad is connected to the driven circuit, the first diode 144a, 144b may be used as a transmitting/receiving switch. In this manner, the limiter module may attenuate leaked signals but may not attenuate "genuinely" received signals that should be forwarded to receiving circuitry, e.g. the LNA 150.

[00049] According to still an embodiment, the exposed pad is connectable to ground and/or to an electrically driven circuit.

[00050] As explained above, the exposed pad may be either connected to ground or connected to a driven circuit. Depending on which alternative, the first diode first diode 144a, 144b operates as a passive or an active limiting component. An active limiting component differs from a passive limiting component in that it may be able to stand different signal input power. When the first diode first diode 144a, 144b operates as a passive limiting component, then it may stand input signal power of X Watts, e.g. 40 W. When the first diode 144a, 144b operates as an active limiting component, then it may stand input signal power of Y Watts, e.g. 70 W, wherein Y>X. Thus, when the first diode 144a, 144b operates as an active limiting

component it may be able to stand higher signal input power than when the first diode 144a, 144b operates as a passive limiting component. The first diode 144a, 144b may further provide a good heat sing power and by used as a switch, when the first diode 144a, 144b operates as an active limiting component.

[00051 ] According to a further embodiment, the limiter module comprises a capacitance 143a, 143b arranged in the transmission line 142a, 142b between the input 141 a, 141 b of the channel and the first diode 144a, 144b. [00052] The capacitance 143a, 143b is used to isolate, or block, any DC component of the leaked signal. All the capacitors have no effects on RF signals.

[00053] According to still an embodiment, the limiter module comprises a capacitance 149a, 149b arranged in the transmission line 142a, 142b between the second diode and the output 141 aa, 141 bb of the channel after the connection to ground.

[00054] This capacitance 149a, 149b has the same function as the capacitance 146a, 146b and the capacitance 143a, 143b, i.e. isolating, or blocking, any DC component of the leaked signal and leaving RF signals unaffected.

[00055] Embodiments herein also relate to a transceiver comprising a limiter module as described above.

[00056] Figure 1a illustrates an exemplifying embodiment of a transceiver 100. Comprised in the transceiver is the limiter module 140 arranged in the signal path between the antenna 1 10 and circulator 120 and the LNA 150. It shall be pointed out that either both the antenna 1 10 and the circulator 120 may be comprised in the transceiver 100 or may be coupled to the transceiver 100. That is, even though figure 1 a illustrates an example of the transceiver wherein the circulator 120 is comprised in the transceiver and the antenna is not, this does not have to be the case. The transceiver 100 in this example if further illustrated comprising a coupler 130, a resistance 195 a coupler 160, a further resistance 190 and further receiving circuits 170. However, this is merely an exemplifying illustration and the

transceiver may comprise other and/or additional components than illustrated in figure 1 a.

[00057] Figure 1 a, illustrates that a signal may be received by means of an antenna 1 10 which then first passes a circulator 120. The circulator has three connections, a first to the antenna 1 10, a second to a coupler 130, and a third to a transmitting part, or power amplifier, PA, 180. The circulator operates in such a manner that a signal being received on the third connection, i.e. from the PA 180 is outputted on the first connection, i.e. forwarded to the antenna 1 10. A signal being received on the first connection, i.e. from the antenna 1 10, is outputted on the second connection, i.e. forwarded to the coupler 130. However, the circulator 120 is not perfect and thus parts of the signal transmitted from the PA 180 leak to the second connection and are thus outputted towards the coupler 130. In order to protect components of the receiving parts of the transceiver 100, e.g. a Low Noise Amplifier, LNA 150, the limiter module 140 is arranged in a path between the circulator 120 and the LNA 150.

[00058] The transceiver may have the same possible advantage as provided by the limiter module. One possible advantage is that the limiter module may be more reliable than a transmission-reception switch under unexpected interference.

Another possible advantage is that the performance may be improved with regard to radio link performance at up to half the input power. The heat sink may be better and the total parasitic effects may be decreased. The limiter module may increase flexibility of the transceiver without requiring bias control and driven circuits, which in turn may reduce cost. With bias control, the limiter module may operate as a switch, wherein receiving signal path may be selected according to different function needs.

[00059] According to an embodiment, as described above, the transceiver further comprises an LNA, wherein the limiter module is arranged between an antenna comprised in, or connectable to, the transceiver and the LNA.

[00060] According to yet an embodiment, the transceiver further comprises a capacitance 143a, 143b arranged between the antenna and the limiter module.

[00061 ] Capacitance 143a, 143b is used to isolate, or block, any DC component of the leaked signal. All the capacitors have no effects on RF signals. Looking at figure 1 a, the transceiver may further comprise a coupler 130 arranged between the antenna 1 10 and the limiter module 140, wherein the capacitance 143a, 143b is arranged between the coupler 130 and the limiter module 140.

[00062] According to still an embodiment, the transceiver further comprises a capacitance 149a, 149b arranged between the limiter module and the LNA 150. [00063] The capacitance 149a, 149b has the same functions as the other capacitances described above, namely to block any possible DC current, DC current being a DC component.

[00064] Figure 2 is an exemplifying illustration of an envelope the limiter module 140 of figures 1 b, 1 c and 1 d. The envelope of the limiter module is illustrated comprising 16 pins and ground. Pin 5 is the input of one channel of the limiter module and, referring to figure 1 a, is connected to the coupler 130. Likewise, pin 8 is the input of another channel of the limiter module and, referring to figure 1 a, is connected to the coupler 130.

[00065] Pin 13 and pin 16 are the respective outputs of the two channels of the limiter module and referring to figure 1 a, are connected to the LNA 150.

[00066] Pins 2 and 1 1 are connected to the exposed pad of the limiter module, also referred to as biasing.

[00067] The rest of the pins are not connected and the envelope of the limiter module further comprises a ground, GND, which is also the heat sink of the limiter module.

[00068] Figure 3 is an exemplifying illustration of the limiter module with low radio frequency power.

[00069] This limiter module has very small insertion loss when input power is less than OdBm.

[00070] Figure 4 is an exemplifying illustration of the limiter module with high radio frequency power.

[00071 ] Figure 4 corresponds to the limiter module 140 of figure 1 c.

[00072] Figure 5 is an exemplifying illustration of a circuit matched with different frequencies. [00073] This is an illustration of how to use the limiter module on different frequency spans by adjusting the matching line.

[00074] Figure 6 illustrates graphs of protector circuit S-parameters when the input power level for B39 is low. S-parameters come from the S-matrix (also known as the scattering matrix), which describes the performance of a radio frequency component. B39 stands for Band 39 which is 1880 MHz to 1920 MHz.

[00075] From the graphs in figure 6, it can be seen that the insertion loss is very small for a received signal.

[00076] Figure 7 illustrates graphs of protector circuit S-parameters when the input power level for B39 is high.

[00077] From the graphs in figure 7, it can be seen that the isolation is very high when the power of the received signal is high.

[00078] Figure 8 illustrates graphs of protector circuit S-parameters when the input power level for B41 is low. B41 stands for Band 41 which is 2.48GHz-2.7GHz.

[00079] From the graphs in figure 8, it can be seen that the insertion loss on this frequency band is very small.

[00080] Figure 9 illustrates graphs of protector circuit S-parameters when the input power level for B41 is high.

[00081 ] From the graphs in figure 9, it can be seen that the isolation on this frequency band is very high.

[00082] Breakdown voltage is used to calculate power compression point.

Region thickness is one of the concerns of switch time or recover time. Thermal impedance and power dissipation are used to calculate power handling

capability. Different from RADAR system, transmit duty cycle of Time Division, TD, communication system can be assumed to be 100%. [00083] Limiter chips CLA4608 and CLA4601 from Skyworks are chosen for an example of the limiter module described above. From the datasheet of these chips, input power for 1 dB loss is 26dBm for CLA4608, 12dBm for CLA4601 . Maximum pulsed input power for CLA4601 is 47dBm, which is larger than the output at max pulsed input of CLA4608. Because the transmission duty cycle of TD communication system is very high, maximum Continuous Wave, CW, input power is used for power capacity calculation for passive use. Maximum power leakage of CLA4601 according to datasheet is 20dBm. But as most power is rejected by CLA4608, leakage power to CLA4601 would be less than 30dBm. As a result, the maximum power transmitted to LNA would be less than 17dBm. This power level is safe for many LNA modules.

[00084] With bias on, i.e. when the exposed pad is connected to the driving circuit, this limiter diode, i.e. the first diode, may be seen as PIN diode for power handling calculation and the isolation would be more than 40dB. Less power dissipation and more isolation mean that this limiter module may stand higher power input.

[00085] When the exposed pad is short to ground, GND, the balanced limiter module may stand about maximum 40W input power at the radio frequency input port in figure 5. It means that even when the antenna port is open, the limiter module may stand about 50W TX output power. By the antenna port being open means that 1 10 of figure 1 is not assembled or connected. The port 1 of 120 may thus be called open. When the exposed pad is connected to the driven circuit, power dissipation on the diode can be calculated follow equation 1 .

[00086] V_p and l_p is the peak voltage/current passing through the diode. R_th, thermal resistance of the CLA4608 is 15°C/W for continuous wave power.

Temperature increase in diode junction is given by equation 2.

Τ=Ρ₀ R_th (2) [00087] Life time of the diode can be calculated by equation 3. K is Boltzmann constant, T is diode junction temperature in kelvin, A=3.56 X 10^"17h, Q=2.942645 X 10^"19.

Q_

t_M (T) = Ae^kT

^{M J} (3)

[00088] To guarantee the life time of diode junction, the highest temperature should be controlled between 105~140°C. This limiter circuit can stand about 150W continuous wave power at the RF input port in figure 5. The life time of this component can be more than 9 X 10⁵h.

[00089] A balanced limiter circuit with this limiter module is used to verify radio frequency performance at different frequency bands. Part 4 in figure 5 illustrates the impedance matching parts. Matching circuits may be adjusted for different frequency bands.

[00090] From 1880MHz to 1920MHz, balanced limiter circuit's insertion loss may be less than 0.1 dB, Return Loss, RL, better than 35dB. Isolation may be 46dB at most. From 2496MHz to 2696MHz, the insertion loss may be less than 0.15dB, RL may be better than 30dB. Isolation may be as high as 49dB. The performance may be guaranteed at different frequency bands. The RL is an example of an S-parameter. By isolation is meant the ability to attenuate a power of a signal.

[00091 ] While the embodiments have been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent upon reading of the specifications and study of the drawings. It is therefore intended that the following appended claims include such alternatives, modifications, permutations and equivalents as fall within the scope of the embodiments and defined by the pending claims.

Claims

1 . A limiter module (140) adapted for use in a transceiver and adapted for reducing leakage of a transmitted signal, the limiter module (140) comprising at least two channels, wherein each channel comprises:

at least two diodes (144a, 147a, 144b, 147b), a first diode (144a, 144b) and a second diode (147a, 147b), connected in parallel to each other along a transmission line (142a, 142b) between an input (141 a, 141 b) and an output (141 aa, 141 bb) of the channel,

- one capacitance (146a, 146b) arranged in the transmission line between the two diodes,

wherein the transmission line (142a, 142b) is arranged with a connection (148a, 148b) to ground between the second diode (147a, 147b) and the output of the channel (141 aa, 141 bb), and with a connection (145a, 145b) to an exposed pad between the first diode (144a, 144b) and the capacitance (146a, 146b).

2. The limiter module (140) according to claim 1 , wherein the connection to ground (148a, 148b) between the second diode and the output of the channel is provided with an inductance (148aa, 148bb).

3. The limiter module (140) according to claim 1 or 2, wherein the connection (145a, 145b) to the exposed pad between the first diode and the capacitance is provided with an inductance (145aa, 145bb).

4. The limiter module (140) according to any of claims 1 -3, wherein the exposed pad is connectable to ground and/or to an electrically driven circuit.

5. The limiter module (140) according to any of claims 1 -4, further comprising a capacitance (143a, 143b) arranged in the transmission line (142a, 142b) between the input (141 a, 141 b) of the channel and the first diode (144a, 144b).

6. The limiter module (140) according to any of claims 1 -5, further comprising a capacitance (149a, 149b) arranged in the transmission line (142a, 142b) between the second diode and the output (141 aa, 141 bb) of the channel after the connection to ground.

7. A transceiver comprising a limiter module (140) according to any of claims 1 -6.

8. The transceiver according to claim 7, further comprising a Low Noise Amplifier, LNA, wherein the limiter module is arranged between an antenna comprised in, or connectable to, the transceiver and the LNA.

9. The transceiver according to claim 8, further comprising a capacitance (143a, 143b) arranged between the antenna and the limiter module.

10. The transceiver according to claim 8 or 9, further comprising a capacitance (149a, 149b) arranged between the limiter module and the LNA.