RF modulator device

Abstract

A radio frequency modulator (1-3) device comprises a baseband stage (1), a mixer stage (2) and a radio frequency stage (3). The baseband stage (1) comprises: an input line for receiving an input current (10) representing a baseband input signal; baseband transistors (11, 12) for passing some or all of the input current (10) between their first and second terminals; an electrical connection (13) between the input line and control terminals of the baseband transistors (11, 12); and an output line connected to the control terminals. The mixer stage (2) receives a signal (BB_I) from the baseband stage (1). p ,BB_I n ) and mixes it with the RF local oscillator signal to generate a RF mixing signal (V_RF p , V_RF n ). The RF stage (3) receives the RF mixing signal (V_RF p , V_RF n ), the RF mixing signal (V_RF p , V_RF n ) is applied to the control terminal of the radio frequency transistor (30, 31) so that it passes the radio frequency output current (I_RF) between its first terminal and the second terminal p , I_RF n ), and the RF output current (I_RF p , I_RF n ) as the output signal (RF out ) output.

Description

Background Art

[0001] The present invention relates to a radio frequency (RF) modulator device.

[0002] RF modulators are used in radio transmitters to up-convert electrical baseband signals to radio frequencies. The resulting electrical RF signals can be passed to a suitable radio antenna for transmission as radio waves. The baseband signal can encode data using one or more of phase, frequency, and amplitude modulation, such as using phase shift keying (PSK) or frequency shift keying (FSK).

[0003] The RF modulator mixes the baseband signal with a periodic signal generated by a local oscillator (LO) at the RF carrier frequency. The mixing process is intentionally nonlinear to generate sum and difference components at radio frequencies that are dependent on the input signal. However, in addition to this desired mixing effect, it is also desirable that the RF modulation device be as linear as possible so that it generates minimal intermodulation distortion, which would otherwise result in out-of-band emissions.

[0004] It is known to implement a highly linear transmitter using an 8-phase mixer in an attempt to reduce the 3rd and 5th order RF harmonics at the output of the mixer output, which in turn reduces the 3rd and 5th order side intermodulation products CIM3 and CIM5 generated at the input of the RF amplifier stage. However, the use of an 8-phase mixer results in considerable complexity, current consumption, and die area.

[0005] The present invention provides a novel RF modulator design that can provide high linearity without the need for such a complex mixer. Summary of the invention

[0006] From a first aspect, the present invention provides a radio frequency modulator device, comprising:

[0007] Baseband level;

[0008] mixer stages; and

[0009] RF level,

[0010] Among them, the baseband stage includes:

[0011] an input line for receiving an input current representing a baseband input signal;

[0012] a baseband transistor arranged to pass some or all of the input current between a first terminal and a second terminal of the baseband transistor;

[0013] an electrical connection between the input line and a control terminal of the baseband transistor; and

[0014] an output line connected to a control terminal of a baseband transistor;

[0015] Among them, the mixer stage:

[0016] arranged to receive a signal from an output line of a baseband stage; and

[0017] configured to mix the received signal with a radio frequency local oscillator signal to generate a radio frequency mixed signal; and

[0018] Among them, RF level:

[0019] arranged to receive the radio frequency mixed signal from the mixer stage;

[0020] including radio frequency transistors;

[0021] configured to apply the RF mixing signal to the control terminal of the RF transistor to cause the RF transistor to pass an RF output current between the first terminal and the second terminal of the RF transistor; and

[0022] An output line is included for outputting the RF output current as a RF output signal.

[0023] From a second aspect, the invention provides a radio transmitter arrangement comprising such a radio frequency modulator arrangement.

[0024] It will thus be seen that according to the invention, the control terminal of a first closed-loop (e.g. diode-connected) transistor in the baseband stage is electrically coupled via an up-converting mixer stage to the control terminal of a second transistor that controls the flow of current in the RF output signal. This arrangement can effectively operate as a current mirror, the entire modulator being a current mirror, across the mixer stages. The baseband transistor acts as a diode-connected input transistor of the current mirror, while the RF transistor acts as a mirrored output transistor.

[0025] It has been found that this design provides analog predistortion through the current mirror linearization principle, which can provide highly linear operation even for relatively simple passive mixers, such as a 4-phase passive mixer. When implemented as an integrated circuit, for example on a single silicon chip, the modulator does not require a large area and can have low current consumption.

[0026] In one set of embodiments, the baseband transistor and the radio frequency transistor are field effect transistors (FETs); the first terminal and the second terminal are drain and source, and the control terminal is a gate. In another set of embodiments, the baseband transistor and the radio frequency transistor are bipolar transistors; the first terminal and the second terminal are collector and emitter, and the control terminal is a base.

[0027] The baseband transistors may be identical or similar to the RF transistors. This may provide accurate current mirroring performance on the modulator. They may have the same voltage or current gain. In some embodiments, both the baseband transistor and the RF transistor are FET transistors, for example, both are MOS transistors, such as NMOS transistors. They may have the same gate width and / or gate length and / or oxide thickness and / or threshold voltage. In embodiments where both the baseband and RF transistors are bipolar junction transistors (BJTs), they may have the same base thickness and / or collector-base junction area and / or emitter-base junction area. The "identical" here preferably means at least identical within manufacturing tolerances. This is because good linearity can be achieved when completely similar baseband and RF transistors are used. However, in some embodiments, "identical" may mean within 5% or 10%. If the transistors are not similar, analog pre-distortion may occur in the baseband stage, which cannot be properly eliminated in the RF stage portion, resulting in a smaller linear mixing result.

[0028] The baseband stage may include a plurality of baseband transistors, such as a group of transistors arranged in parallel, arranged together to pass some or all of the input current. The corresponding control terminal of each of the group of baseband transistors may be connected to the input line. Additionally or alternatively, the RF stage may include a plurality of RF transistors, such as a group of transistors arranged in parallel, arranged together to pass the RF output current. The corresponding control terminal of each of the group of RF transistors may be arranged to receive the RF mixing signal. The individual baseband transistors and RF transistors in each group may be the same, that is, both groups of transistors are constructed using the same unit element. This may allow some embodiments of the RF modulator to provide a predictable gain to the mirror current, rather than uniformly mirroring the input current. By using the same unit transistors in both groups, the gain may be conveniently determined as the ratio of the number of activated transistors in each group. The baseband stage may include one or more switches for switchably enabling and disabling one or more of the plurality of baseband transistors (i.e., for connecting it to the current path and excluding it from it). The RF modulator device may provide an interface (e.g., a register interface accessible by a processor via a bus) for controlling how many of the plurality of baseband transistors are enabled. Additionally or alternatively, the RF stage may include one or more switches for switchably enabling and disabling one or more of the plurality of RF transistors. The RF modulator device may provide an interface (e.g., a register interface) for controlling how many of the plurality of RF transistors are enabled. This may allow programmatic control of the gain level. In some embodiments, the gain may be selected between a set of values, which may include one or more of: one, one or more values ​​greater than one (i.e., amplification), and one or more fractional values ​​(i.e., attenuation). This may allow the RF modulator to support a wide gain control range, making it well suited for use with radio protocols such as LTE (Long Term Evolution). In some embodiments, these values ​​are rational numbers.

[0029] The baseband transistor can be a baseband transconductor (G m ) unit. Baseband G m The unit can provide resistive degeneration by grounding the baseband transistor through a resistive element. The RF transistor can be an RF transconductor (G m ) unit. m The unit can provide resistive negative feedback by connecting the RF transistor to ground through a resistive element. Each resistive element can be a dedicated element, such as a resistor or a MOS transistor biased in the linear (triode) region, or can be provided in combination with other features, such as a resistive enable switch (i.e., for enabling G m A switch of a cell, wherein the resistor is incorporated into the switch).

[0030] The electrical connection between the input line and the control terminal of the baseband transistor may be a direct connection, but in a preferred set of embodiments the connection comprises an amplifier. The amplifier may be a voltage amplifier, such as an operational amplifier. The amplifier may thus close the loop of the baseband transistor. The amplifier may ensure that the input current entering the baseband stage has only a small impedance, so that high linearity is more easily obtained in the circuit driving the baseband current. Due to its buffering capability, the amplifier may help avoid crosstalk (so-called tilt) between the in-phase and quadrature parts of the baseband part, and may ensure good gain of the mixer stage.

[0031] The amplifier may have a first input connected to the input line and an output connected to a control terminal of the baseband transistor. It may have a second input (e.g., a differential input) for connecting to a reference voltage. The reference voltage may define the voltage at the input line. The amplifier may be configured to drive the control terminal of the baseband transistor to a voltage at which all input current from the input line is drawn by the baseband transistor or a group of baseband transistors.

[0032] Since the control terminals of the baseband transistors are also connected to the mixer, the amplifier can also drive the mixer stage, as well as driving the baseband transistors. Therefore, the amplifier output can present a pre-distorted voltage waveform that is required to produce a similar high linearity current when driven to the RF transistor (on the mirror side of the current mirror). The presence of a mixer stage between the diode-connected baseband transistor and the mirror RF transistor of the current mirror enables the input current with a highly linear baseband component to be transferred to the RF while maintaining high linearity.

[0033] The amplifier can help compensate for the capacitive losses between the baseband transistors and the RF transistors. It can also reduce the impedance seen by the current source that provides the input current to the input line within the bandwidth of the amplifier. The smaller impedance can ease the requirements on the driver module and achieve high linearity in the current source.

[0034] The baseband stage may include a capacitor connected to the output line. The capacitor may be arranged to provide a transient current to the output line. This is useful to prevent voltage drops on the output line during fast switching within the mixer and RF stages when the bandwidth of the amplifier may prevent the amplifier from being able to react quickly enough to transients during switching operations.

[0035] The RF modulator may be a differential modulator. The baseband stage may include a pair of input lines for receiving a differential input current and a pair of output lines for outputting a differential output signal to a mixer stage. It may include respective baseband transistors and may optionally include a respective amplifier connected to each input line. It may include a respective capacitor connected to each output line.

[0036] The RF modulator may be a quadrature modulator. The baseband stage may include an in-phase portion and a quadrature portion. The two portions may be identical. Each portion may include a baseband transistor and an amplifier. When configured to receive a differential input signal, each portion may include a pair of baseband transistors and a pair of amplifiers.

[0037] The mixer can be a passive mixer. It can be a voltage mixer. It can be a quadrature mixer. It can be a four-phase mixer, but it can also be a two-phase mixer or a mixer that uses more phases.

[0038] In some embodiments, the baseband stage may include one or more filters for filtering the input signal. The filtering may be provided on the input line, before the baseband transistors, or may be provided around the amplifier.

[0039] The RF modulator may be configured to operate at gigahertz frequencies, for example to receive a local oscillator signal at approximately 2.4 GHz.

[0040] The RF stage may be an RF amplifier stage. The RF transistor or a set of connected RF transistors may provide amplification or attenuation of current, for example by having a different effective gate area (when using FETs) or different effective base-emitter and base-collector areas (when using BJTs) than the baseband transistors. In some embodiments, the gain of the modulator may be an integer or rational number; this may be achieved by providing the same transistors in the baseband stage and the RF stage with integer ratios.

[0041] The modulator may be implemented as an integrated circuit (IC) device, such as on a system on a chip (SoC).

[0042] The radio transmitter device may include a power amplifier connected to the output line of the RF stage. The transmitter device may include an antenna connected directly or indirectly to the output line. The device may include any one or more of the following: a power supply, such as a battery; one or more processors for generating a baseband input signal; a crystal oscillator, for example for generating a local oscillator signal or signals; a user interface; discrete components; integrated components; etc.

[0043] The radio modulator may be adapted to modulate LTE (Long Term Evolution) signals and / or Bluetooth TM (Bluetooth) signals, such as Bluetooth Low Energy TM (Bluetooth Low Energy) signals, and / or any other radio signals, for radio transmission. The radio transmitter means may comprise an LTE (Long Term Evolution) radio transmitter.

[0044] Circuits referred to herein may include open circuit and closed circuit parts, ie they are not necessarily connected to a power supply.

[0045] The features of any aspect or embodiment described herein may be applied to any other aspect or embodiment described herein where appropriate. Where different embodiments or groups of embodiments are mentioned, it should be understood that these embodiments or groups of embodiments are not necessarily different and may also overlap. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Certain preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0047] Figure 1 is a circuit diagram of a baseband stage of a differential quadrature RF transmitter modulator embodying the present invention;

[0048] Figure 2 is a circuit diagram of a passive mixer stage of a differential quadrature RF transmitter modulator;

[0049] Figure 3 is a circuit diagram of an RF amplifier stage of a differential quadrature RF transmitter modulator;

[0050] Figure 4 is a circuit diagram of a single-ended RF transmitter modulator embodying the present invention; and

[0051] Figure 5 It is a circuit diagram of the baseband level based on the traditional design principle;

[0052] Figure 6 is a graph comparing output current and third order intermodulation products (CIM3) versus baseband level for an RF transmitter modulator of conventional design and embodying the present invention. DETAILED DESCRIPTION

[0053] Figures 1 to 3 A differential quadrature RF transmitter modulator circuit 1-3 embodying the present invention is shown.

[0054] Figure 1 The baseband (BB) level shown in 1 Figure 2 The four-phase passive mixer stage 2 shown outputs a differential baseband signal BB_I n BB_I p BB_Q n BB_Q p Mixer stage 2 converts the differential RF signal V_RF p 、V_RF n Output to Figure 3 RF amplifier stage 3 is shown.

[0055] The entire RF modulator circuit can be implemented in silicon. It may form part of a larger circuit, such as a CMOS radio-on-chip device, which may include one or more processors, memory, buses, etc. It may be an LTE (Long Term Evolution) integrated circuit chip or a Bluetooth Low Energy TM Part of an integrated circuit chip. The modulator may be part of a larger electronic device, such as a networked sensor device, e.g. connected to a power source, external antenna, etc.

[0056] In the detailed description Figures 1 to 3 Before discussing the detailed differential quadrature (IQ) implementation, first consider Figure 4 It is useful to illustrate a simpler single-ended implementation which nevertheless operates on the same basic principles.

[0057] Figure 4 and Figures 1 to 3 Both of the RF transmitter modulators operate using a buffered current mirror concept where the baseband stage and the RF amplifier stage act together as a current mirror, across the RF mixer stage, so that the current of the baseband input signal is mirrored (same or amplified or with fractional gain) at the RF output of the RF amplifier stage.

[0058] exist Figure 4 In the present invention, a current source 40 provides an analog input signal. This signal can encode binary data for transmission over the radio. An NMOS "baseband" or "diode-connected" transistor 41, an NMOS "radio frequency" or "mirror" transistor 42, and an operational amplifier 43 are used together as a current mirror. The diode-connected transistor 41 is connected in a closed-loop configuration through the operational amplifier 43. The operational amplifier 43 can drive the diode device gate of the diode-connected transistor 41 to a voltage such that all the input current I from the current source 40 is absorbed by the diode transistor 41.

[0059] Although the exemplary embodiments described herein employ field effect transistors, it will be appreciated that in alternative embodiments bipolar transistors may instead be used.

[0060] First, consider the following situation: the series switch 45 between the two transistors 41 and 42 is turned on, and the ground switch 46 is turned off, so that the voltages at points A and B are equal (ie, have a common node voltage).

[0061] Figure 4The output of the current mirror circuit will be equal to the input current multiplied by the gate area of ​​the mirror transistor 42, divided by the gate area of ​​the diode-connected transistor 41. The mirror transistor 42 and the diode-connected transistor 41 typically have the same channel length L, and therefore the current gain will be proportional to the ratio of their respective gate widths W. The mirror transistor 42 may be equal to the diode-connected transistor 41, or it may be larger, such as having an integer multiple of the gate area, so that the modulator amplifies the input signal at the RF output, or it may be smaller so that the modulator provides a fractional gain.

[0062] If a direct current (DC) source is mirrored, the operational amplifier 43 will help compensate for potential gate leakage currents in the gates of the transistors 41, 42. However, when the operational amplifier 43 is used to mirror an alternating current (AC) signal, as in this article, the role of the operational amplifier 43 is more important. In this case, the operational amplifier 42 will compensate for the capacitive losses that occur at the node between the two transistors 41, 42. The larger the device, that is, the larger the diode-connected transistor 41 and the mirror transistor 42, the larger the capacitive load in the node will be. In addition, when the operational amplifier 43 closes the diode loop, it effectively reduces the impedance seen by the input current source 40 within the bandwidth of the operational amplifier 43. Smaller impedance can ease the requirements on the driving module and achieve high linearity in the current source design.

[0063] Since the driving input source is a current, the diode-connected transistor 41 does not have a linear transfer function from the gate-source voltage (Vgs) to the drain current (Id). If the input current source 40 drives a perfect sinusoidal signal, i.e., without harmonic components, the node voltage at point A (equal to B) will be a pre-distorted voltage, and when driven to a device similar to the diode-connected transistor 41 (such as the mirror transistor 42), the output of the similar device will be close to perfect linearity. In this buffered current mirror arrangement, the output current will be a very close replica of the input current I, scaled only in amplitude. In practice, the characteristics of the operational amplifier 43, such as bandwidth and DC gain, will determine the extent to which the AC output current simulates the AC input current.

[0064] Consider now switches 45, 46 located at the node between diode-connected transistor 41 and mirror transistor 42. When off, series switch 45 disconnects the gate of mirror transistor 42 from diode-connected transistor 41 and operational amplifier 43, while ground switch 46 grounds the gate of mirror transistor 42 when on. Switches 45, 46 are configured to always be in opposite states to each other. In use, their states are switched at a radio frequency (e.g., 2.4 GHz) under the control of a local oscillator (LO) (not shown). In this way, a baseband input signal I can be mixed to a radio frequency band centered around the LO switching frequency.

[0065] When the series switch 45 is non-conducting, the gate is discharged through the ground switch 46. Therefore, the effective load of the mirror transistor 42 increases with the switching frequency, because the gate capacitance needs to be charged at each transition (i.e., each time the series switch 45 is turned on). However, the operational amplifier 43 can provide the average current required due to this switching operation, even at high frequencies. The bandwidth (BW) of the operational amplifier 43 is limited, so it reacts slowly to transients during the switching operation; however, the capacitor 44 can provide the necessary transient current to achieve fast switching of the mirror transistor 42.

[0066] Now consider Figures 1 to 3 , which uses the same mirror image concept but is implemented in a differential IQ modulator circuit.

[0067] Figure 1 A baseband (BB) stage 1 is shown which provides high linearity. The baseband stage 1 is connected to an RF amplifier stage 3 via a mixer stage 2, such as Figure 2 and Figure 3 as shown in .

[0068] The baseband stage 1 has an in-phase (I) section that receives a differential (p and n) in-phase (I) current signal from an in-phase differential signal source 10; and an identical quadrature phase (Q) section that receives a differential (p and n) quadrature (Q) current signal from a quadrature differential signal source 110. The baseband stage 1 can be connected to any suitable source external to the RF modulator. For example, it can be connected to a digital baseband stage that provides the I and Q signals to the baseband stage 1 through corresponding digital-to-analog converters (DACs) (not shown). The digital baseband stage can generate the I and Q signals by encoding digital data received from a processor or other source. Filtering can optionally be provided before the current sources 10, 110.

[0069] The transconductance (G m ) units 11, 12 provide very linear positive (p) and negative (n) differential IQ currents I p ,I n Each G m The units 11, 12 contain corresponding NMOS transistors. Each Gm unit 11, 12 may also contain a grounded resistor to implement resistive negative feedback. These resistors are not required, but may help provide improved linearity and / or better matching with the RF amplifier. m Units 11, 12 may optionally include a plurality of G connected in parallel. m Each G in the group mThe cell may have a corresponding enabling switch device, for example comprising an enabling transistor (not shown). This may allow the total gate area of ​​the diode-connected transistors 11, 12 to be programmably controlled. These G m Unit (or G m Unit group) 11, 12 plays a role in Figure 4 The diode connected transistor 41 has the same effect as in the single ended design.

[0070] A pair of operational amplifiers 13 and 14 corresponds to Figure 4 The operational amplifier 43, and the pair of capacitors 15, 16 correspond to Figure 4 The outputs of the operational amplifiers 13, 14 supported by the capacitors 15, 16 are passed to the mixer stage 2 as the baseband signal BB_I p BB_I n , are used to drive the IQ modulator switches 20-23 in mixer stage 2. These in turn drive the RF amplifier 3.

[0071] The quadrature section similarly comprises a pair of operational amplifiers 113, 114 arranged to switch on the respective G m Unit or G m The group of units 111, 112. A pair of capacitors 115, 116 is a quadrature phase output signal BB_Q p and BB_Q n To provide transient current support, they are provided to the IQ modulator switches 120-123 in mixer stage 2.

[0072] Figure 2 A mixer stage 2 is shown, which includes a passive voltage mixer. It includes separate I and Q sections, each receiving an input from a four-phase local oscillator (LO) (not shown) oscillating at a radio frequency (e.g., about 2.4 GHz). The four-phase LO signal is applied to the gates of four transistors 20, 21, 22, 23 in the I section, and to the gates of a group of four transistors 120, 121, 122, 123 in the Q section. Transistors 20-23 and 120-123 mix the baseband signal and the LO signal to generate a differential RF output. The I and Q outputs are combined at the output of the mixer stage 2 to provide a single differential RF signal V_RF p 、V_RF n , the signal is passed to the RF amplifier 3.

[0073] Mixer stage 2 switches the outputs of different baseband op amps 13, 14, 113, 114 to the inputs of RF amplifier stage 3 at different times. Therefore, each time the mixer switches 20-23, 120-123 are switched, the input parasitic capacitances of RF amplifier stage 3 are charged to a new voltage. The charging is done by the op amps 13, 14, 113, 114, but also by the op amp output capacitors 15, 16, 115, 116.

[0074] Figure 3 The RF amplifier stage 3 is shown, which converts the differential RF signal component V_RF p 、V_RF n to the corresponding transconductance (G m ) In the unit groups 30 and 31, each group includes one or more G connected in parallel. m Unit, each G m The size of the unit is similar to that of a single G in the baseband stage 1 m The units are similar or identical. These G m The unit generates an amplified differential output current I_RF p 、I_RF n In some embodiments, this can be output as a differential signal, for example, to a positive supply on both the p and n output branches for an inductor or resistor. The differential output can be provided to a differential power amplifier. However, in this embodiment, the output current I_RF p 、I_RF n The single-ended RF signal RF is generated by the balun 32. out . Then the RF out Connected to a suitable on-chip or off-chip radio antenna (not shown) for transmission, for example via an optional filtering section to a suitable power amplifier stage (not shown).

[0075] G in RF amplifier stage 3 m Each transistor in unit 30, 31 is connected to G in baseband stage 1. m Each transistor in cells 11 , 12 , 111 , 112 is similar, ie, has the same or similar gate width, length and thickness, and the same or similar threshold voltage.

[0076] In some embodiments, the activated G in baseband stage 1 m The number of cells 11, 12, 111, 112 and / or the number of active G in the RF amplifier stage 3 m The number of units 30, 31 can be variable, for example by means of an enabling switch ( Figure 1 This can be used to control the gain of the RF modulator, which will depend on the active G in the RF amplifier stage 3.m Units 30, 31 are relative to the activated G in baseband stage 1 m The relative number of units 11, 12, 111, 112. The RF transmitter modulator 1-3 may include a register interface and suitable control circuitry (not shown) which may be written to via a data bus (e.g. by a processor) to control how many of the plurality of baseband stage and / or amplifier stage transistors are enabled.

[0077] The outputs of the operational amplifiers 13, 14, 113, 114 in the baseband stage 1 exhibit a very linear baseband current draw (I p ,I n , Q p , Q n ) The predistortion voltage required. Due to the switching, the same voltage waveform is applied to the input of the RF amplifier stage 3 in segments. Therefore, G in the RF amplifier stage 3 m Units 30, 31 produce highly linear output currents, but at radio frequencies.Thus, the use of baseband stage 1 in combination with mixer stage 2 and RF amplifier stage 3 preserves the inherent linearity of the current mirrors in baseband to RF frequency conversion.

[0078] This can be achieved by combining the new baseband stage 1 with Figure 5 This is shown in comparison to the simpler design shown. Figure 6 The graph in shows the performance difference between an embodiment of the present invention and a simpler design.

[0079] Figure 5 A basic baseband stage 5 is shown having an in-phase (I) section fed by a differential in-phase (I) signal source 50 and a quadrature-phase (Q) section fed by a differential quadrature-phase (Q) signal source 150. The in-phase section has an output amplified or buffered differential baseband signal BB_I n BB_I p The differential output operational amplifier 51 of FIG. 5 is shown in FIG. 5 . Each output lead is connected to a respective capacitor 52, 53 which can provide additional transient current to the mixer stage 2 when required. The quadrature (Q) section is similarly arranged, with an output amplified differential baseband signal BB_Q n BB_Q p The differential output operational amplifier 151 is supported by two capacitors 152 and 153.

[0080] Baseband stage 5 can be connected to Figure 2 and Figure 3 The mixer stage and RF amplifier stage are similar to those shown, but require the use of AC coupling capacitors between the mixer and RF amplifier stages and provide a separate bias for the RF amplifier stage.

[0081] However, such a modulator may still have suboptimal linearity even when using highly linear voltage sources 50, 150 in the baseband stage 5. The baseband harmonics modulated around the LO harmonics may be relatively high, resulting in significant CIM (cross-intermodulation) products and ACPR (adjacent channel power ratio).

[0082] In contrast, Figure 1 The novel baseband stage 1 is able to have significantly lower unwanted side intermodulation products (CIM) and intermodulation distortion (IMD) products. However, the complexity of the baseband stage 1 is roughly the same level as a simple voltage mode passive mixer IQ modulator and significantly lower than the complexity of an 8-phase modulator. The current consumption is also reasonable.

[0083] Figure 6 shows an RF modulator with a simple voltage mode drive design, with baseband stage 5 and Figure 5 1 ) shows simulation results comparing the third order CIM (CIM3) products when sweeping the baseband level between a) a similar and ii) a novel RF modulator implemented using the current mirror method disclosed in this article.

[0084] The top curve 60 depicts the output current of the RF amplifier for the two designs; the two designs are almost identical and therefore appear as a single line. This shows that the two modulators provide the same output level and therefore it is possible to compare their linearity.

[0085] The two lower curves 61, 62 show the respective CIM3 products. The higher of the two lower curves 61 relates to the conventional design, while the lower curve 62 relates to the new design. It can be seen that the new design improves CIM3 by about 13 dB at the corresponding output power level.

[0086] In addition to these linearity improvements, the new design provides additional options for gain control, as the gain can be controlled by varying the active G in the baseband stage 1. m The number of units, for example, by adding an additional G m The current mirror ratio is adjusted by switching cells into or out of the circuit. Activating more G at the baseband stage 1 m The unit reduces the current mirror ratio and lowers the gain, thereby reducing the active G at the baseband stage 1. m The number of cells increases the current mirror ratio and improves the gain.

[0087] G in RF amplifier 3 m The units operate at radio frequencies and they are preferably small in size so as to have small parasitic effects. m The units 11, 12, 111, 112 are also preferably of small size.

[0088] Having small devices can make the design susceptible to mismatch effects. When mismatch exists, BB_I p and BB_I n Between and BB_Q p and BB_Q n There will be a DC offset voltage between the RF amplifier stage 3 and the RF amplifier stage 3. The DC offset voltage may cause carrier leakage or local oscillator feedthrough (LOFT) at the output of the RF amplifier 3. This can be mitigated by providing DC offset calibration or compensation using any appropriate technique, at least in some embodiments. The offset may occur due to baseband stage mismatch, and the compensation method can be performed at the baseband stage 1. The mismatch at the RF amplifier stage 3 is not transferred to the RF, but is only visible at the DC current. If a current mode mixer is used, as in some embodiments, the offset can be calibrated separately for each gain step, although the level of carrier leakage may be small to begin with.

[0089] Those skilled in the art will recognize that the present invention has been described by way of the description of one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible within the scope of the appended claims.

Claims

1. A radio frequency modulator device, comprising: Baseband level; Mixer stage; as well as RF level, Wherein, the baseband stage includes: an input line for receiving an input current representing a baseband input signal; a baseband transistor arranged to pass some or all of said input current between a first terminal and a second terminal of said baseband transistor; An electrical connection between the input line and a control terminal of the baseband transistor; and an output line connected to the control terminal of the baseband transistor; Wherein, the mixer stage: arranged to receive a signal from said output line of said baseband stage; and configured to mix the received signal with a radio frequency local oscillator signal to generate a radio frequency mixed signal; Wherein, the radio frequency level: arranged to receive said radio frequency mixed signal from said mixer stage; including radio frequency transistors; configured to apply the RF mixing signal to a control terminal of the RF transistor to cause the RF transistor to pass an RF output current between a first terminal and a second terminal of the RF transistor; and comprising an output line for outputting the RF output current as a RF output signal; and The baseband transistor and the radio frequency transistor have the same voltage gain or the same current gain.

2. The radio frequency modulator device according to claim 1, wherein: The baseband stage, the mixer stage and the radio frequency stage are integrated on a single silicon chip.

3. The radio frequency modulator device according to claim 1, wherein: The baseband transistor and the radio frequency transistor are field effect transistors, the first terminal and the second terminal are a drain terminal and a source terminal, and the control terminal is a gate terminal.

4. The radio frequency modulator device according to claim 3, wherein: The baseband transistor has the same gate width and gate length as the radio frequency transistor.

5. The radio frequency modulator device according to claim 1, wherein: The baseband transistor is an element of a baseband transconductance unit, and wherein the baseband transconductance unit comprises a resistive element for grounding the baseband transistor to provide resistive degeneration.

6. The radio frequency modulator device according to claim 1, wherein: The baseband stage comprises a set of baseband transistors, the set of baseband transistors comprising the baseband transistor and one or more further baseband transistors arranged in parallel with the baseband transistor, wherein a respective control terminal of each of the set of baseband transistors is connected to the input line.

7. The radio frequency modulator device according to claim 6, wherein: The baseband stage comprises one or more switches for switchably enabling and disabling one or more of the set of baseband transistors.

8. The radio frequency modulator device according to claim 1, wherein: The radio frequency transistor is an element of a radio frequency transconductance unit, and wherein the radio frequency transconductance unit comprises a resistance element for grounding the radio frequency transistor to provide resistance degeneration feedback.

9. The radio frequency modulator device according to claim 1, wherein: The RF stage comprises a set of RF transistors including one or more further RF transistors arranged in parallel with the RF transistor, wherein a respective control terminal of each of the set of RF transistors is arranged to receive the RF mixing signal.

10. The radio frequency modulator device according to claim 9, wherein: The radio frequency stage comprises: one or more switches for switchably enabling and disabling one or more of the set of radio frequency transistors.

11. The radio frequency modulator device according to claim 1, wherein: The baseband stage includes a plurality of baseband transistors; The RF stage includes a plurality of RF transistors; as well as Each of the plurality of baseband transistors and the plurality of radio frequency transistors is a field effect transistor, wherein all the field effect transistors have the same gate area.

12. The radio frequency modulator device according to claim 11, wherein: The RF modulator device provides an interface for controlling how many of the plurality of baseband transistors are enabled to pass the input current and / or for controlling how many of the RF transistors are enabled to pass the RF output current.

13. The RF modulator device according to claim 1, configured or controllable to provide a gain from the input current to the RF output current, the gain being a rational number.

14. The radio frequency modulator device according to claim 1, wherein: The electrical connection between the input line and the gate of the baseband transistor comprises an amplifier.

15. The radio frequency modulator device according to claim 14, wherein: The amplifier is an operational amplifier.

16. The radio frequency modulator device according to claim 14, wherein: The amplifier is configured to drive the gate of the baseband transistor to a voltage at which the entire input current from the input line is drawn by the baseband transistor, or to drive the gates of a group of baseband transistors to a voltage at which the entire input current from the input line is drawn by the group of baseband transistors, wherein the group of baseband transistors includes the baseband transistor and one or more additional baseband transistors arranged in parallel with the baseband transistor.

17. The radio frequency modulator device according to claim 1, comprising: A capacitor connected to the output line is used to provide a transient current to the output line.

18. The radio frequency modulator device according to claim 1, wherein: The radio frequency modulator means is a differential modulator means, and wherein the baseband stage comprises: a pair of input lines for receiving a differential input current; a pair of output lines for outputting a differential output signal to the mixer stage; and A respective baseband transistor or group of baseband transistors is connected to each input line.

19. The radio frequency modulator device according to claim 1, wherein: The radio frequency modulator arrangement is a quadrature modulator arrangement and wherein the baseband stage comprises an in-phase section and a quadrature section, each section comprising a respective baseband transistor of a set of baseband transistors.

20. The radio frequency modulator device according to claim 1, wherein: The mixer stage comprises a passive voltage mixer.

21. The radio frequency modulator device according to claim 1, wherein: The mixer stage comprises a four-phase quadrature mixer.

22. A radio transmitter device comprising a radio frequency modulator device according to any one of claims 1 to 21.

23. The radio transmitter device of claim 22, comprising a power amplifier and an antenna, wherein: The power amplifier is arranged to receive and amplify the radio frequency output current, and wherein the antenna is arranged to transmit the amplified radio frequency output signal as a radio signal.

24. Radio transmitter means according to claim 23, configured to transmit a Long Term Evolution radio signal using the radio frequency modulator means.

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