WO2009121861A2

WO2009121861A2 - Radio frequency modulator

Info

Publication number: WO2009121861A2
Application number: PCT/EP2009/053782
Authority: WO
Inventors: Xin He; Jan Van Sinderen; Manel Collados Asensio; Nenad Pavlovic
Original assignee: Nxp B. V.
Priority date: 2008-04-02
Filing date: 2009-03-31
Publication date: 2009-10-08
Also published as: WO2009121861A3

Abstract

The present application relates to a radio frequency modulator comprising at least two unit cells, wherein at least one unit cell comprises a local oscillator input terminal. The at least one unit cell is configured to generate at least one up-converted output signal depending on a local oscillator signal. The at least one unit cell comprises at least one data input terminal, wherein the data input terminal is arranged to receive at least a first data signal. The at least one unit cell is configured such that the generating of the up-converted output signal is deactivatable at least depending on the first data signal. The present application relates also to a transmitter, a method for generating an up-converted output signal and a computer readable medium having a computer program stored thereon.

Description

Radio frequency modulator

TECHNICAL FIELD

The present application relates to radio frequency modulator comprising at least two unit cells, wherein at least one unit cell is configured to generate at least one up- converted output signal. The present application relates also to a transmitter, a method for generating an up-converted output signal and a computer readable medium having a computer program stored thereon.

BACKGROUND

It is an ongoing concern in modern communication systems, in particular in wireless communication systems, to improve the power efficiency of transmitter devices. For instance, in mobile devices or the like, energy supply may be limited, and thus, a reduced power consumption is required. A further concern in modern communication systems is to increase the data rate. One possibility to achieve the requirements is the use of suitable radio frequency modulators.

In general, for improving the data rate, modulation types with non-constant envelopes can be used. However, problems may arise by using high efficient amplifiers for amplifying the signal being transmitted to a suitable transmit power due to the non-constant envelope of the signal. For instance, inphase-quadrature (IQ) transmitters can be used together with external power amplifier. Drawbacks of such transmitters are the need of a low pass filter causing a large chip area, low power efficiency and a limited bandwidth.

Transmitters achieving better results comprise direct digital modulators, like digital radio frequency (RF) modulators. Such a radio frequency modulator, as depicted in Fig. 10, can use a linear interpolation current steering digital analogue converter (DAC) 70 for driving the mixing device 72 directly with a base band current signal. The mixing device may be a Gilbert cell which is configured for up converting a base band signal, like a current. The Gilbert cell comprises a current source circuit 76 comprising two transistors, a data switching circuit 78 comprising four transistors and the output terminals 74.

A digital radio frequency modulator according to prior art may comprise an array of multiple unit cells, as shown in Fig. 10, driven by a quadrature local oscillator (LO) signal. The summation of the unit cell output currents may generate the modulated radio frequency signal. However, the power efficiency in such a direct digital radio frequency modulator is low. Furthermore, the local oscillator leakage is also a problem, which is responsive for degrading the error vector magnitude (EMV). An improved power efficiency can be achieved using a polar transmitter.

However, such a polar transmitter comprises the issue of spectral re-growth. Hence, for reducing spectral re-growth, extra filtering is required, and thus, the required chip space is increased.

It is one object of the present application to provide a radio frequency modulator with increased power efficiency. It is a further object of the present application to reduce local oscillator leakage. Another object of the present application is to improve the error vector magnitude. A further object is to avoid spectral re-growth and extra filtering. Another object is to reduce required chip space

SUMMARY

These and other objects are solved by a radio modulator comprising at least two unit cells, wherein at least one unit cell comprises a local oscillator input terminal. The at least one unit cell is configured to generate at least one up-converted output signal depending on a local oscillator signal. The at least one unit cell comprises at least one data input terminal, wherein the data input terminal is arranged to receive at least a first data signal. The at least one unit cell is configured such that the generating of the up-converted output signal is deactivatable at least depending on the first data signal.

The radio frequency modulator according to the present application may be a direct digital radio frequency modulator. Such a radio frequency modulator according to the present application can be used in any kind of transmitting device. In particular, the radio frequency modulator can be used in a transmitter for wireless communication systems.

The radio frequency modulator comprises at least two unit cells. It shall be understood that the radio frequency modulator may comprise a plurality of unit cells. The unit cell may be a mixing device, like an electronic multiplying mixing device or an analogue multiplier device for currents. For example, the present unit cell may be a modified Gilbert unit cell.

At least one of the unit cells comprises a local oscillator input terminal. The local oscillator input terminal may be provided to supply the unit cell with a suitable local oscillator signal. The local oscillator signal may be generated by an appropriate oscillator or oscillator circuit.

Furthermore, the at least one unit cell of the radio frequency modulator is configured to generate at least one up-converted output signal depending on the local oscillator signal applied at the local oscillator input terminal. For instance, a base band signal can be up-converted using a local oscillator signal to an up-converted output signal. The up- converted output signal may comprise a desired frequency and, in particular, the up- converted output signal may be an up-converted output current. Furthermore, each unit cell may comprise at least one output terminal, at which the generated up-converted output signal is applied. The unit cell may generate the up-converted output signal at least depending on the polarity of the local oscillator signal. A simple mixing for achieving the desired up- converted output signal is given.

In addition, the unit cell comprises at least a second input terminal, in particular, a data input terminal. The data input terminal may be arranged to receive a data signal. More particularly, at least one first data signal can be received via the data input terminal by the unit cell. It shall be understood that the data input terminal may be provided to receive more data signals as well as more than one data input terminal can be arranged at the unit cell.

It is found according to the present application that the power efficiency of a radio frequency modulator can be significantly increased, in case at least one unit cell of the radio frequency modulator is deactivatable. According to prior art, a radio frequency modulator comprising multiple unit cells, each of these unit cells generates always an up- converted output signal during operation. Contrary to expectations, it is found according to the present application that it is not necessary that all unit cells of a radio frequency modulator generate always a current during operation to achieve the desired radio frequency modulated signal. The radio frequency modulator according to the present application comprises at least one unit cell, which is deactivatable at least depending on a first data signal. In other words, the respective unit cell can be turned off using the first data signal applied at the data input terminal. By way of example, the current path through the unit cell to its output terminal can be locked depending on the first data signal, in particular depending on an especially value of the first data signal.

It shall be understood that at least both unit cells, preferably all unit cells of the radio frequency modulator may comprise the same configuration providing for that each unit cell of the radio frequency modulator can be deactivated. Furthermore, the data signals used to control each unit cell may differ from each other.

The present application provides for a significant increase of current efficiency of a radio frequency modulator. The power efficiency of the present radio frequency modulator is also increased, while the EVM is not degraded and spectral re-growth issues are avoided.

At least one unit cell of the radio frequency modulator may comprise, according to a further embodiment of the present application, a current source circuit. The current source circuit may be provided to generate a current. The current source circuit can be implemented using a transistor driven by a suitable bias voltage, a controllable current source or the like. Furthermore, the generated current may be up-converted to the up-converted output signal of the unit cell at least depending on the local oscillator signal. A simple implementation of the unit cell, and thus, of the total radio frequency modulator is given. Furthermore, according to another embodiment, at least one unit cell of the radio frequency modulator may comprise a local oscillator switching circuit, which may be connectable to the local oscillator input terminal, wherein the local oscillator switching circuit may be configured to drive the up-conversion of the generated current. The local oscillator switching circuit may comprise a number of suitable switching units, like transistors. The switching units and the local oscillator switching circuit respectively can be driven by the local oscillator signal. Depending on the polarity of the local oscillator signal, the switching units may be conductive or non-conductive. More particularly, a certain current path through the local oscillator switching circuit may depend on the polarity of the local oscillator signal.

A simple possibility to affect the polarity of the up-converted output signal is the use of a data switching circuit. According to another embodiment of the present application, at least one unit cell of the radio frequency modulator may comprise a data switching circuit which may be configured to set at least the polarity of the up-converted output signal. The data switching circuit can be connected to the local oscillator switching circuit. Thereby, it is possible to connect the data switching circuit to outputs or inputs of the local oscillator switching circuit. The data switching circuit may also comprise suitable switching units, like transistors. These switching units can be driven by at least one data signal, like the first data signal or a further data signal. More particularly, a current flow through a switching unit can be controlled via the respective data signal. According to a further embodiment of the present application, the current source circuit can be connected to the data switching circuit and/or the local oscillator switching circuit.

In a further embodiment of the radio frequency modulator according the present application, a generating circuit can be arranged, wherein the generating circuit may be configured to generate at least the first data signal depending on the information being transmitted. A suitable signal generator, in particular a digital signal generator can be employed. Each unit cell can be supplied by a specific first data signal wherein each first data signal ay depends on the information being transmitted. A digital first data signal may be advantageous for driving switching units, and more particularly, to switch them on and/or off. In particular, switching units included within the data switching circuit, local oscillator switching circuit and/or current source switching circuit can be deactivated using the first data signal.

Moreover, it is found that the need of the activation of a particular unit cell of the radio frequency modulator of a plurality of unit cells may depend on the information being transmitted. However, it shall be understood that, according to further variants of the present application, the first data signal may also depend on further system parameters or other parameters.

Furthermore, the generating circuit according to another embodiment of the application may be configured to generate at least a second data signal depending on the information being transmitted. The second data signal may be also a digital signal. It may be also possible that more than two data signals are generated according to further variants of the present application. In addition, the second data signal can be used for setting the polarity of the output signal of the particular unit cell of the radio frequency modulator. By way of example, the data switching circuit can be driven at least by the second data switching circuit for setting the polarity. It is also possible, according to a further embodiment that the first data signal and the second data signal both are used for controlling the activatability and deactivatability respectively of a unit cell. By way of example, it may be necessary that the first data signal and the second data signal must comprise a particular value for deactivating the particular unit cell. Using two data signals may cause a better flexibility and may reduce components, like transistors, required within the unit cell and radio frequency modulator respectively.

According to a further embodiment, the generating circuit may be a thermometer decoder. A thermometer decoder can be easily used to generate at least the first data signal, especially a digital data signal, depending on the thermometer code for driving a plurality of unit cells. However, according to further variants of the present application all data signals can be generated by the thermometer decoder as well as it is possible that more than one thermometer decoder is provided.

As already mentioned, the first and the second data signals may be digital signals. According to another embodiment, at least one of the first data signal and the second data signal may be unipolar encoded data signal and/or signed data signal. The advantage of a unipolar encoded data signal may be the simplicity of the signal. Such a signal merely comprises the values 0 and 1. Other values of a unipolar encoded data signal may be not possible. A signed data signal may comprise a positive signal, like +1 and a negative signal - 1. However, it shall be understood that according to further variants of the present application, different encodings of the data signals, like NRZ, RZ or the like can also be used.

The data switching circuit and the local oscillator switching circuit may comprise at least two transistors. A transistor may be especially suitable since the switching mechanism of a transistor can be easily controlled and the required chip space may be low. It is possible to implement different kinds of transistors, like MOSFETs or bipolar transistors. By way of example, NMOS transistors or PMOS transistors can be implemented.

For deactivating a particular unit cell of the radio frequency modulator and avoiding the generating of an output current by the respective unit cell, it is found that it is possible to control the current source circuit and/or local oscillator switching circuit and/or data switching circuit of the unit cell accordingly. More particularly, at least one of these circuits can be deactivated at least depending on the first data signal, and thus, deactivating the respective unit cell. Furthermore, it may be also possible to attach an additional device for deactivating the unit cell.

According to an embodiment of the present application, the data switching circuit can be connected to the data input terminal and may be configured to be deactivatable depending on the first data signal and/or the second data signal. It may be possible to design the data switching circuit such that all current paths through the data switching circuit are non-conductive depending on the first data signal. In particular, the locking of the current paths can be obtained depending on a particular value of the first data signal. A current path from the current source circuit to the output terminals of the respective unit cell can be turned off. The unit cell may not generate an up-converted output signal and current respectively. Another possibility is to use the first data signal in connection with the second data signal for avoiding a current flow through the data switching circuit. The data signals can be applied at the data input terminal and decoded such that the data switching circuit can be turned off depending on a specific combination of values of both data signals. It shall be understood that more than two data signals can be used for controlling the data switching circuit. For instance, each transistor included in the data switching circuit can be controlled and turned off by a different data signal. The power efficiency of the radio frequency modulator can be increased by simple means.

Furthermore, it may be also possible to control the local oscillator switching circuit depending on the first data signal and/or the second data signal according to another embodiment. For instance, the local oscillator switching circuit can be controlled and deactivated via the data switching circuit. According to a further embodiment of the present application, the current source circuit can be connected to the data input terminal and may be configured to be deactivatable at least depending on the first data signal. More particularly, the current source can be deactivated and a current flow to the output terminal of the respective unit cell can be avoided depending on the first data signal. The current source circuit may comprise a number of switching units, like suitable transistors, which can be driven by at least the first data signal such that a current cannot flow to the subsequent arranged circuits, like the data switching circuit, the local oscillator switching circuit or the like. By way of example, the current source circuit can be controlled such that the output terminal of the current source terminal is at ground potential. It may be also possible to use more than one data signal for controlling the current source circuit. Deactivating the respective unit cell by deactivating the current source circuit can be easily performed.

As already mentioned before, the current source circuit can be connected to the data switching circuit and/or the local oscillator switching circuit. The current generated by the current source circuit can flow through one, both or none of these circuits. Moreover, the current may flow from the tail of the unit cell through both stacked circuits to the output terminals of the unit cell. It is found that the power efficiency of the radio frequency modulator can be further increased by increasing the voltage efficiency. The voltage efficiency can be increased, in case merely one transistor stage is arranged between the current source circuit and output terminals of a unit cell. According to a further embodiment of the present application, the current source circuit can be also connected to at least one transistor output array. At least one output transistor array comprising two transistors connectable to at least one part of the local oscillator switching circuit and to the current source may increase voltage efficiency. The current may merely flow form the current source to the output terminals of the unit cell through one switching unit, like a transistor. The local oscillator leakage can be reduced as well as the degrading of the EVM can be avoided. The radio frequency modulator according to another embodiment of the present application can be implemented in CMOS technology, bipolar technology, BiCMOS technology, GaAs, discrete device and/or a combination of them. For example, the CMOS technology can be used, since the required chip space may be low. For instance, NMOS and/or PMOS transistors can be implemented as switching units within the respective circuits of a unit cell. However, according to different system requirements, the implementation of the radio frequency modulator in other technologies may be also suitable. Furthermore, as already mentioned, a plurality of unit cells can be employed within the radio frequency modulator according to the present application. Thereby, the employed unit cells are deactivatable and during operation, it may be possible that at least one unit cell of the multitude of unit cells is deactivated. Such a radio frequency modulator may comprise an increased power efficiency, since the voltage efficiency as well as the current efficiency can be significantly increased compared to radio frequency modulator of prior art.

What is more, according to a further embodiment of the present application, the radio frequency modulator can be configured to generate a radio frequency output signal at least depending on the up-converted output signal of at least one unit cell. The radio frequency modulator may be configured to generate a radio frequency output signal depending on the up-converted output signals, like the current signals, of two unit cells, preferably of all unit cells. In particular, radio frequency modulator can be configured to sum the output currents of all activated unit cells for generating the desired radio frequency output signal. A suitable radio frequency output signal can be generated providing for a high data rate.

In another embodiment of the radio frequency modulator according to the present application, at least one unit cell can be configured to generate the inphase component of the radio frequency signal and at least the further unit cell can be configured to generate the quadrature component of the radio frequency signal. I/Q modulation types are especially suitable to increase the data rate. In particular, the two unit cells can be driven by a quadrature local oscillator signal applied at the respective local oscillator input terminals. For instance, the two unit cells can be driven by four local oscillator signals comprising a phase shift of 90 degree to each other. Summing the up-converted output currents of both unit cells, the desired radio frequency signal can be generated a simple manner. According to a further embodiment of the present application, the radio frequency modulator may comprise a unit cell matrix, wherein the unit cell matrix may comprises N x N unit cells stated above. The unit cells can be arranged in N columns and N rows. The data rate can be significantly increased. Furthermore, since the unit cells may be deactivatable, the power efficiency of the radio frequency modulator can be increased. It may be also possible, according to further variants of the present application that M x N unit cells are arranged within the unit cell matrix.

In addition, the power efficiency of the radio frequency modulator can be further improved by using a column buffered local oscillator driving strategy. According to a further embodiment, the radio frequency modulator may comprise a column buffer circuit, wherein the column buffer circuit may be configured to drive the local oscillator signals of at least one column of the unit cell matrix. As stated above, a column may comprise N unit cells. The column buffer can be used for controlling the local oscillator signals. For each column of the unit cell matrix, a column buffer can be arranged. The column buffer can be configured such that not all unit cells included in the column are supplied with the local oscillator signal. Merely the activated unit cells can be supplied with the local oscillator signal. The column buffer can be controlled by a suitable data signal which can be generated by the thermometer decoder. Loss of power caused by parasitic effects can be avoided. The local oscillator leakage can be significantly reduced. Furthermore, degrading of the EVM can be avoided. Voltage drops caused by parasitic effects can be significantly reduced. Such a strategy may be in particular suitable in high power applications.

A further aspect of the present application is a transmitter comprising a radio frequency modulator stated above. For instance, the transmitter may comprise a direct digital radio frequency modulator or a digital radio frequency polar modulator according to the present application. Such transmitters can be employed into mobile phones and used within wireless communication systems.

Another aspect of the application is a method for generating a local oscillator output signal. The method comprises generating at least one local oscillator signal for driving a local oscillator switching circuit, generating a current by a current source circuit, wherein the current is up-converted depending on the local oscillator signal, generating at least one first data signal, and deactivating the generating of the up-converted output signal at least depending on the first data signal. Another aspect of the present application is a computer readable medium having a computer program stored thereon. The computer program comprises instructions operable to cause a processor to perform the above-mentioned method.

These and other aspects of the present patent application become apparent from and will be elucidated with reference to the following Figures. The features of the present application and of its exemplary embodiments as presented above are understood to be disclosed also in all possible combinations with each other.

BRIEF DESCRIPTION OF THE DRAWINGS In the Figures show:

Fig. 1 a first embodiment of the unit cell of the radio frequency modulator according to the present application,

Fig. 2 a first embodiment of the radio frequency modulator according to the present application, Fig. 3 a second embodiment of the radio frequency modulator according to the present application,

Fig. 4 a third embodiment of the radio frequency modulator according to the present application,

Fig. 5 a second embodiment of the unit cell of the radio frequency modulator according to the present application,

Fig. 6 a third embodiment of the unit cell of the radio frequency modulator according to the present application,

Fig. 7 an embodiment of the unit cell of an envelope radio frequency modulator according to the present application, Fig. 8 a diagram of a thermometer decoded unit cell matrix of the radio frequency modulator according to the present application,

Fig. 9 an embodiment of the column buffer circuit of the radio frequency modulator according to the present application,

Fig. 10 a Gilbert unit cell according to prior art. Like reference numerals in different Figures indicate like elements.

DETAILED DESCRIPTION OF THE DRAWINGS In the following detailed description of the present application, exemplary embodiments of the present application will describe and point out a radio frequency modulator with at least two unit cells comprising increased power efficiency.

Fig. 1 shows a first simplified embodiment of the unit cell of the radio frequency modulator according to the present application. The shown unit cell 2 can be deactivated depending on at least a first data signal via data input terminal 7.

As can be seen from Fig. 1, the unit cell comprises a current source circuit 4, a local oscillator switching circuit 6 and a data switching circuit 8. Furthermore, the unit cell 2 may generate an up-converted output signal, which is applied at terminal 22. A base band signal, preferably a digital base band signal may drive the data switching circuit 8. This signal can be also fed to the data switching circuit via data input terminal 7. The use of further input terminals may be also possible. The local oscillator switching circuit 6 can be driven by a suitable local oscillator signal applied at the local oscillator input terminal 5. Moreover, local oscillator switching circuit 6 may be configured for up-converting a digital base band signal to a suitable radio frequency. Suitable oscillators, like voltage controlled oscillators (VCO) or the like can be employed (not shown). The provided switching circuits 6, 8 may comprise suitable switching elements, like transistors, which are configured to be conductive or not conductive depending on the polarity or logical values of the local oscillator signal and digital base band signal respectively. A possible implementation of the unit cell shown in Fig. 1 is depicted in Fig.

2. Fig. 2 shows a first simplified embodiment of the radio frequency modulator according to the present application, like a digital direct radio frequency modulator, comprising a plurality of unit cells 2. Two of these unit cells 2 are depicted in depth, wherein both unit cells 2, especially the local oscillator switching circuits 6 can be driven by a quadrature local oscillator signal for realizing an inphase and quadrature component respectively. More particularly, one unit cell 2 may be driven by the signal cos(wLot) and the further unit cell 2 may be driven by the signal sin(wLot), wherein W_LO is the frequency of the signal. The respective local oscillator signals can be supplied to the unit cells 2 via the local oscillator input terminal 5, wherein the specific electrical communication with the local oscillator circuit is not shown for saving the clarity of Fig. 2. Same applies for the data input terminal 7 and the respective electrical connections to the components arranged within the unit cell 2 as well as for the generating circuit 3 and the respective electrical connections to the unit cells 2.

In the following, the layout of one unit cell 2 is explained in detail. In the present embodiment, all transistors 20a to 2Oi are formed as NMOS transistors, and thus, each transistor 20a to 2Oi can be switched on, in case a positive value is applied at their gate terminals. It shall be understood that other kinds of transistors, like PMOS transistors, bipolar transistors or the like, can be also employed.

The current source circuit 4 in the shown embodiment comprises three transistors 20a to 20c and one inverter 18. Furthermore, the current source circuit 4 comprises two input terminals 10 and 12. At terminal 12, a bias voltage Vbias can be applied for generating the required current using transistors 20a and 20b. The further terminal 10 can be connected to the data input terminal 5 and can be supplied by a first data signal D. The first data signal D can be driven and generated by the generating circuit 3. The generating circuit 3 may be a suitable signal generator, preferably a digital signal generator.

In this embodiment, the output of transistor 20a can be connected to the data switching circuit 8, and more particularly, to the input terminals of transistors 2Od and 2Oe arranged within the data switching circuit 8. Furthermore, the data switching circuit 8 comprises a further inverter 18 and a further input terminal 14. Input terminal 14 can communicate with data input terminal 7 or another data input terminal. Furthermore, via input terminal 14 the data switching circuit 8 can be supplied by a second data signal S, which can be signed data providing the polarity of the input data. Also the second data signal S can be can be driven and generated by the generating circuit 3. The generating circuit 3 may be configured to generate data signals, in particular all data signals, for all unit cells 2 depending on the information being transmitted. It shall be understood that according to further variants of the present application, more than one generating circuit can be arranged, for instance a particular generating circuit for each unit cell, which can be controlled by a suitable controlling device or the like.

In addition, the local oscillator switching circuit 6 comprises two transistor pairs 2Of, 2Og and 2Oh, 2Oi. While the local oscillator signal is applied at input terminals 16 of the local oscillator switching circuit 6, the two outputs of the data switching circuit 8 are connected to the further input terminals of the transistor pairs in the depicted way. The local oscillator switching circuit 6 may generate depending on the local oscillator signal, an analogue output signal comprising a positive or negative amplitude. The output signal may be a current signal, in particular, the desired up-converted output signal.

The radio frequency modulator comprises two output terminals 24. These output terminals 24 can be connected to a further amplifying unit or directly to an antenna device (not shown) for transmitting the generated radio frequency signal comprising the information being transmitted to a suitable counterpart station or the like. In the following the functioning of the unit cell 2 and the total radio frequency modulator is pointed out in detail. The shown radio frequency modulator may be implemented for realizing a direct digital radio frequency modulator according to the present application comprising an array of unit cells 2. The unit cells 2 can be driven by local oscillator signals and digital data signals. The summation of the unit cells up-converted output currents may generate the desired modulated radio frequency signal. This modulated radio frequency signal can be additional amplified and subsequent transmitted or directly transmitted via a suitable antenna or the like to a counterpart station. It is found according to the present application that instead to prior art radio frequency modulators, it is not necessary that all unit cells always generate an output current during operation. Particular unit cells can be deactivated at least depending on the information being transmitted.

More particularly, according to the present embodiment, the current source circuit 4 can be controlled such that the respective unit cell 2 can be deactivated. The current source circuit 4 can be driven by the first data signal D, wherein this first data signal D may be a unipolar encoded signal, comprising the logical values 1 and 0. When the first data signal D comprises the value 1 , transistor 20b is turned on and transistor 20c is turned off, and thus, the current source circuit 4 and the unit cell 2 respectively is turned on and activated respectively. For the case, the value of the first data signal D is 0, transistor 20b is turned off and transistor 20c is turned on, and thus, the current source circuit 4 and the unit cell 2 respectively is turned off. Since the unit cells 2 are not always generating an output current signal during operation, the current efficiency of the total radio frequency modulator, and thus, the power efficiency can be significantly increased.

In the following, the functioning of the unit cell 2 for the case that the unit cell 2 is activated is shortly described. When the current source circuit 4 is activated, an output current can be generated depending on the local oscillator signals and the second data signal S. The differential local oscillator signals may drive the double balanced structure to up- convert the signed base band signal onto a suitable frequency.

More particularly, for generating an up-converted output signal, a current flow must be realized from the current source circuit 4 to the output terminals of the respective unit cell 2. Thus, the current source circuit 4 must be activated. In this case, the second data signal S determines in connection with the polarity of the local oscillator signal the polarity of the up-converted output signal, and more particularly, the second data signal S may control transistors 2Od and 2Oe of the data switching circuit. Then, the differential local oscillator signals may drive the double balanced structure of the local oscillator switching circuit 6 comprising the four transistors 2Of to 2Oi such that the signed base band signal can be up- converted. Subsequently, the up-converted output currents of all unit cells 2 may be summed for obtaining the desired radio frequency output signal at terminals 24 of the present radio frequency modulator. Furthermore, it may be advantageous to reduce the power for driving the local oscillator switching circuit 6. A possible implementation of an embodiment of the radio frequency modulator according to the present application, wherein the power for driving the local oscillator switching circuit 6 is reduced, is depicted in Fig. 3. The embodiment shown in Fig. 3 differs from the embodiment depicted in Fig. 2 merely in one item. Thus, merely the differential between both embodiments is elucidated. As can be seen from Fig. 3, the local oscillator switching circuit 6a and the data switching circuit 8a are exchanged. Thereby the functioning of each unit cell 2a can be maintained, while the power efficiency can be increased. Merely two transistors 2Od, 2Oe are implemented within the local oscillator switching circuit 6a and these transistors 2Od, 2Oe are directly coupled to the current source circuit 4. The power required for driving the local oscillator switching circuit 6a can be reduced.

It shall be understood that the first and second data signals D and S generated for a particular unit cell 2a may differ from the data signals D and S generated for the further unit cells 2a. In other words, each unit cell 2a can be driven by a different first and second data signal D and S. Moreover, it shall be denoted that the current efficiency can be further improved when standards with a large crest factor in modulation are used.

In a further embodiment of the radio frequency modulator according to the present application, the number of essential transistors can be reduced and the power efficiency can be further improved. Fig. 4 shows a third embodiment of the radio frequency modulator according to the present application. The current source circuit 4a according to this embodiment comprises merely one transistor 20a. At its terminal 12, a suitable bias voltage Vbias is applied for generating the required current. However, the shown current source circuit 4a cannot be deactivated contrary to the current source circuits according to the previous embodiments. The subsequent arranged local oscillator switching circuit 6a corresponds to the local oscillator switching circuit 6a according to the embodiment illustrated in Fig. 3. The following arranged data switching circuit 8b comprises two input terminals 14a and 14b contrary to merely one input terminal arranged within the previous embodiments. At input terminal 14a, a first data signal Dl can be applied, while at the input terminal 14b, a second data signal D2 can be applied. The first and second data signals Dl and D2 may be driven and generated by the generating circuit 3 and the signed data signals Dl and D2 can be decoded as follows. The polarity of one unit cell 2b may be positive in case, the value of the first data signal Dl is 1 and the value of the second data signal D2 is 0. In case the values of the data signals Dl and D2 are complementary values to the previous case, thus Dl=O and D2=l, the polarity of the unit cell 2b is negative. Furthermore, the respective unit cell 2b according to the present embodiment can be also deactivated at least depending on the first data signal Dl. More particularly, in case, first and second data signals Dl and D2 both comprise the value 0, the unit cell 2b is turned off. Since all transistors arranged within the data switching circuit 8b are formed as NMOS transistors, none of these transistors is conductive and the generating of an up-converted output signal can be avoided. The power efficiency of the present unit cell 2b and the total radio frequency modulator respectively can be significant increased compared to radio frequency modulator according to prior art. It shall be understood that the data signals can be decoded in another way, for instance, in case other kind of transistors are employed within the respective unit cell. It shall be further understood that the generated data signals may depend on the information being transmitted.

In particular, the current efficiency is increased according to the embodiments stated above while the voltage efficiency is remained almost unchanged. It is found, according to the present application that the two stacked switch stages, i.e. the local oscillator switching circuit and the data switching circuit, are responsible for the fact that the voltage efficiency remained almost unchanged. For improving besides the current efficiency also the voltage efficiency, the present application proposes a further embodiment of the unit cell of the radio frequency modulator according to the present application which is shown in Fig. 5. Before elucidating the functioning of the shown embodiment in depth, the layout of the depicted unit cell 2c included within the radio frequency modulated is shortly pointed out. The shown unit cell 2c comprises a plurality of transistors, whereas the transistors in the shown embodiment are formed as PMOS or NMOS transistors. It shall be understood that, according to other variants of the present application, other kinds of transistors can be also employed. A PMOS transistor according to the present application is conductive, in case the signal applied at its gate terminal comprises the value 0.

The unit cell 2c comprises a first transistor array 26, which may act at least partially as the data switching circuit known from the previous embodiments. The transistors included in the transistor array 26 are driven by a second data signal S via input terminal 36. Thereby, two transistors are driven by data signal S and two transistors are driven by the inverted data signal S using the arranged inverter 18. For keeping the clarity of Fig. 5, a generating circuit is not shown. However, it shall be understood that the data signals may be generated in a similar way as stated above and can supplied to the unit cell via data terminal 7. A second transistor array 28 can be driven by the first data signal D via input terminal 34 and an arranged inverter 18. This second transistor array 28 may be also a part of the data switching circuit according to previous embodiments. The transistors included in transistor array 28 are connected to the previous mentioned transistor array 26 and to subsequent arranged transistor pairs 30. The transistor pairs 30 are driven via its gate terminals by the positive local oscillator signal via terminal 38a and by the negative local oscillator signal via terminal 38b. The transistor pairs 30 may act as the local oscillator switching circuits as stated above.

In turn, the outputs of two of the four transistor pairs 30 are each coupled to one output transistor array 32 comprising an output terminal 22a, 22b. The output terminals 22a, 22b can be connected to a bus for generating the radio frequency signal depending on all activated unit cells 2c arranged within the radio frequency modulator. Each of the output transistor arrays 32 are connected to a voltage source circuit 4b. The shown voltage source circuit 4b may be a controllable voltage source.

The functioning of the unit cell 2c can be described as follows. The total unit cell 2c can be deactivated for increasing power efficiency using the first data signal D. In case, the value of the first data signal D is 0, each of the transistors of the transistor array 28 is switched off. Thus, the voltage applied at the gate terminals of the transistors included in the output transistor arrays 32 is zero, and hence, a current does not flow to the output terminals 22a and 22b. In the other case, D=I, the transistor array 28 is conductive and the local oscillator signal can pass depending on the second data signal S to the output transistor arrays 32 for up-converting the current generated by the current source circuit 4b. As can be seen from Fig. 5, the voltage drop can be significantly reduced. Merely one transistor stage, i.e. the output transistor array 32, is arranged subsequently to the current source circuit 4b. The power efficiency can be significantly increased. It shall be further denoted that the local oscillator is isolated from the output terminals 22a, 22b when the unit cell 2c is deactivated. The leakage problem caused by the local oscillator can be reduced as well. It shall be understood that the inverter 18 at terminal 34 can be omitted in case NMOS transistors are employed within the transistor array 28 or a first data signal is generated accordingly.

An alternative embodiment of the unit cell 2c according to Fig. 5 is shown in Fig. 6. As can be seen from Fig. 6, the transistor array 28 shown in the previous embodiment is omitted. The first transistor array 26, which may serve as data switching circuit can be driven via two input terminals 40a and 40b. At input terminal 40a, a first data signal Dl can be applied, while at the further input terminal 40b, a second data signal D2 can be applied. The first and second data signals Dl and D2 may be driven by the generating circuit (not shown) and the signed data signal can be decoded as follows. The polarity of the unit cell 2d may be positive in case, the value of the first data signal Dl is 0 and the value of the second data signal D2 is 1. In case the values of data signals Dl and D2 are complementary values to the previous case, thus Dl=I and D2=0, the polarity of the unit cell 2d is negative. Furthermore, also the unit cell 2d according to the shown embodiment can be deactivated. In case, the first and second data signals Dl and D2 both comprise the value 1, the unit cell 2d is turned off. The generating of the up-converted output signal can be avoided. The power efficiency of the present unit cell 2d and the total radio frequency modulator respectively can be significantly increased compared to radio frequency modulators according to prior art.

For keeping the clarity of Fig. 6, a generating circuit is not shown. However, it shall be understood that the data signals may be generated in a similar way as stated above and can supplied to the unit cell via data terminal 7.

Fig. 7 shows an embodiment of a digital envelope radio frequency modulator according to the present application. The depicted embodiment comprises two transistor pairs 30a serving as local oscillator switching circuits. The first transistor pair 30a can be applied with the positive local oscillator signal via terminal 44a and the further transistor pair 30a can be applied with the negative local oscillator signal via terminal 44b.

Transistor array 26 may serve as data switching circuit, which can be driven by the first data signal D applied at terminal 42 and inverter 18. Furthermore, a current source circuit 4b is also arranged within the shown embodiment. The functioning of the present embodiment is similar to the previous embodiments. When the first data signal D comprises the value 1, the shown unit cell 2e is activated. For the opposite case, D=O, the unit cell 2e is deactivated and the generating of the up-converted output signal can current respectively can be avoided. For keeping the clarity of Fig. 7, a generating circuit is not shown. However, it shall be understood that the data signals may be generated in a similar way as stated above and can supplied to the unit cell via data terminal 7.

What is more, it is found according to the present application that the power efficiency, in particular, in high power applications, can be further improved. The power consumed for driving the local oscillator signals may be high. Furthermore, parasitic effects may also cause a local oscillator leakage. Moreover, the error vector magnitude (EVM), an indicator for the quality of modulation, may be degraded at low power level.

The present application proposes a column buffered local oscillator driving strategy for avoiding or at least reducing the problems stated above. This strategy is pointed out by the aid of Figs. 8 and 9. Fig. 8 shows a diagram of a thermometer decoded unit cell matrix 46, which may comprise N x N unit cells. Furthermore, a thermometer decoder 48, like a binary thermometer decoder can be connected to the unit cell matrix 46 via connections 54 and 56. Thereby, connection 54 may serve for driving the rows of the unit cell matrix 46 while connection 56 may serve for driving the columns of the unit cell matrix 46. The thermometer decoder 48 comprises input terminals 50 and 52, wherein the thermometer decoder 48 can be supplied with a suitable clock signal via terminal 50 and with binary input data via terminal 52.

The thermometer decoded unit cell matrix 46 comprises to further input terminals 58a and 58b serving for the positive local oscillator signal and negative local oscillator signal respectively. The positive part of radio frequency output signal and the negative part of the radio frequency output signal respectively can be applied at terminal 59a and terminal 59b respectively.

Fig. 9 shows a simplified embodiment of the column buffer circuit according to the present application. The column buffer circuit can be provided for the unit cell matrix 46. The input terminals 60a and 60b may serve for supplying the positive and negative local oscillator signal component to the buffer. Moreover, the shown embodiment comprises a further input terminal 64 and two output terminals 62.

According to the present embodiment, the N x N unit cells according to the present application may not be driven directly with the local oscillator signals. The local oscillator signals may pass previously the column buffer circuits. The column buffer circuits can be controlled by a column selection signal via input terminal 64. The column selection signal may be generated by the thermometer decoder 48. The output signals, i.e. the local oscillator signals, can be fed to the N unit cells in the corresponding column, which should be activated at a particular time during operation. Local oscillator leakage can be avoided, since merely the actually activated unit cells are supplied with local oscillator signals. The power efficiency can be increased.

It shall be understood that the radio frequency modulator according to the present application may comprise merely identical unit cells as well as different kinds of unit cells can be combined.

Furthermore, it is readily clear for a person skilled in the art that the logical blocks in the schematic block diagrams may at least partially be implemented in electronic hardware and/or computer software, wherein it depends on the functionality of the logical block and on design constraints imposed on the respective devices to which degree a logical block or algorithm step is implemented in hardware or software. The presented logical blocks and algorithm steps may for instance be implemented in one or more digital signal processors, application specific integrated circuits, field programmable gate arrays or other programmable devices. The computer software may be stored in a variety of storage media of electric, magnetic, electro -magnetic or optic type and may be read and executed by a processor, such as for instance a microprocessor. To this end, the processor and the storage medium may be coupled to interchange information, or the storage medium may be included in the processor.

Claims

CLAIMS:

1. A radio frequency modulator, comprising: at least two unit cells (2, 2a, 2b, 2c, 2d, 2e), wherein at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) comprises a local oscillator input terminal (5), - wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) is configured to generate at least one up-converted output signal depending on a local oscillator signal, wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) comprises at least one data input terminal (7), wherein the data input terminal (7) is arranged to receive at least a first data signal, and wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) is configured such that the generating of the up-converted output signal is deactivatable at least depending on the first data signal.

2. The radio frequency modulator according to claim 1, wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) comprises a current source circuit (4, 4a, 4b) configured to generate at least one current.

3. The radio frequency modulator according to claim 2, wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) comprises: a local oscillator switching circuit (6, 6a) connectable to the local oscillator input terminal (5), wherein the local oscillator switching circuit (6, 6a) is configured to drive an up- conversion of the generated current.

4. The radio frequency modulator according to claim 1, wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) comprises a data switching circuit (8, 8a) configured to set at least the polarity of the up-converted output signal.

5. The radio frequency modulator according to claim 1, further comprising a generating circuit (3) configured to generate at least the first data signal depending on the information being transmitted, wherein the generating circuit (3) is connectable to the data input terminal (7).

6. The radio frequency modulator according to claim 5, wherein the generating circuit (3) is configured to generate at least a second data signal depending on the information being transmitted.

7. The radio frequency modulator according to claim 5, wherein the generating circuit (3) is a thermometer decoder (48).

8. The radio frequency modulator according to claim 6, wherein at least one of the first data signal and the second data signal is at least one of: A) unipolar encoded data signal,

B) signed data signal.

9. The radio frequency modulator according to claim 6, wherein the at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) is deactivatable depending on the first data signal and the second data signal.

10. The radio frequency modulator according to claim 4, wherein the data switching circuit (8, 8a, 8b) and/or the local oscillator switching circuit (6, 6a) comprise at least two transistors (20a, 20b, 20c, 2Od, 2Oe, 2Of, 2Oi, 2Oh).

11. The radio frequency modulator according to claim 6, wherein the data switching circuit (8, 8a, 8b) is connectable to the data input terminal (7), and the data switching circuit (8, 8a, 8b) is configured to be deactivatable depending on the first data signal and/or the second data signal.

12. The radio frequency modulator according to claim 6, wherein the local oscillator switching circuit (6, 6a) is controllable depending on the first data signal and/or the second data signal.

13. The radio frequency modulator according to claim 2, wherein the current source circuit (4, 4a, 4b) is connectable to the data input terminal (7), and - the current source circuit (4, 4a, 4b) is configured to be deactivatable at least depending on the first data signal.

14. The radio frequency modulator according to claim 4, wherein the current source circuit (4, 4a, 4b) is connected to at least one of: A) data switching circuit (8, 8a, 8b),

B) local oscillator switching circuit (6, 6a).

15. The radio frequency modulator according to claim 3, further comprising at least one transistor output array (32), - wherein the transistor output array (32) can be connected to at least a current source circuit (4, 4a, 4b) and at least one part (30) of the local oscillator switching circuit (6, 6a).

16. The radio frequency modulator according to claim 1, wherein the radio frequency modulator is implemented in at least one of:

A) CMOS technology,

B) bipolar technology,

C) BiCMOS technology,

D) GaAs,

E) discrete device,

F) combination of them.

17. The radio frequency modulator according to claim 1, wherein the radio frequency modulator is configured to generate a radio frequency output signal at least depending on the up-converted output signal of the at least one unit cell (2, 2a, 2b, 2c, 2d,

2e).

18. The radio frequency modulator according to claim 1, wherein at least one unit cell (2, 2a, 2b, 2c, 2d, 2e) is configured to generate the inphase component of the radio frequency signal, and at least one further unit cell (2, 2a, 2b, 2c, 2d, 2e) is configured to generate the quadrature component of the radio frequency signal.

19. The radio frequency modulator according to claim 1, further comprising: a unit cell matrix (46), wherein the unit cell matrix (46) comprises N x N unit cells (2, 2a, 2b, 2c, 2d, 2e).

20. The radio frequency modulator according to claim 19, further comprising - a column buffer circuit, wherein the column buffer circuit is configured to drive the local oscillator signals of at least one column of the unit cell matrix (46).

21. A transmitter comprising a radio frequency modulator according to claim 1.

22. A method for generating an up-converted output signal, comprising: generating at least one local oscillator signal for driving a local oscillator switching circuit (6, 6a), generating a current by a current source circuit (4, 4a, 4b), - wherein the current is up-converted depending on the local oscillator signal, generating at least one first data signal, and deactivating the generating of the up-converted output signal at least depending on the first data signal.

23. A computer readable medium having a computer program stored thereon, the computer program comprising instructions operable to cause a processor to perform a method according to claim 22.