Method and system for obtaining maximum gain of a passive upconversion mixer utilized in a transmitter

A RF transmitter is operable to transmit a signal at a frequency specified by the Bluetooth protocol. A passive upconversion mixer, which comprises a pair of MOSFET switches, is utilized inside the RF transmitter. The passive upconversion mixer is operable to receive analog local oscillator (LO) signals to be utilized for controlling operation of each of the pair of MOSFET switches to transmit signals with maximum gain. A MOS threshold voltage VTH and a DC component of a received baseband signal, VBBDC, are determined for each of the pair of MOSFET switches. The determined VTH and the determined VBBDC of the received baseband signal are combined such as VTH+VBBDC and compared with a DC component of the received LO signals, VLODC. The VLODC is set equal to VTH+VBBDC, accordingly, to provide maximum gain from the passive upconversion mixer for signal transmission.

Not applicable.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to communication systems. More specifically, certain embodiments of the invention relate to a method and system for obtaining maximum gain of a passive upconversion mixer utilized in a transmitter.

BACKGROUND OF THE INVENTION

A wireless transmitter transmit wireless signals via a wireless medium and a wireless communication device comprising a receiver is operable to receive and recover the transmitted wireless signals from the wireless medium. The transmitted wireless signals may be distorted and/or otherwise degraded during transmission over the wireless medium. The distortion and/or degradation may occur as a result of factors comprising channel impairments such as noise, signal interference, intersymbol interference and co-channel interference. Accordingly, the transmitter is generally operable to code and/or otherwise process information contained in the transmitted wireless signals so as to mitigate the effects of any actual and/or perceived channel impairments.

Mobile communication devices, such as cellular telephones, personal digital assistants (PDAs), and other communication devices transmit and/or receive communication signals at various radio frequencies. For efficient communication, associated radio frequencies of the transmitted and/or received communication signals are many times higher than corresponding baseband frequencies.

With the rapid growth of wireless communication devices, semiconductor technology has been scaling down to meet the need of a considerable increase in transceiver integration and a reduction in transceiver cost. The need for lower power consumption and higher circuit densities are realized via lowering supply voltages in logic circuits that utilize these semiconductor technologies.

BRIEF SUMMARY OF THE INVENTION

A method and/or system for obtaining maximum gain of a passive upconversion mixer utilized in a transmitter, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and system for obtaining maximum gain of a passive upconversion mixer utilized in a transmitter. In accordance with various embodiments of the invention, a passive upconversion mixer may be utilized in a radio frequency transmitter for transmitting a signal at a frequency specified by, for example, 2.4 GHz as specified by the Bluetooth protocol. The passive upconversion mixer is operable to receive an analog local oscillator (LO) signal from a local oscillator. The passive upconversion mixer comprises a pair of MOSFET switches. The received analog LO signal may be utilized to control operation of each of the pair of MOSFET switches, respectively. The passive upconversion mixer is operable to transmit signals with maximum gain of the passive upconversion mixer. A MOS threshold voltage VTHmay be determined for each of the pair of MOSFET switches, respectively. The passive upconversion mixer is operable to receive an analog baseband signal to the pair of MOSFET switches with the determined MOS threshold voltage VTH. A DC component of the received analog baseband signal, VBB—DC, for each of the pair of MOSFET switches may be determined. A DC component of the received analog LO signals, VLO—DC, may be compared with a combination, for example, a linear combination, of the determined VTHand the determined VBB—DC. The determined DC component of the received analog LO signal may be set to be equal to the combination of the determined MOS threshold voltage VTHand the DC component VBB—DCof the received analog baseband signal VBB(t) for the transmission of the received analog baseband signal based on the comparison.

FIG. 1is a block diagram of an exemplary communication device that utilizes a dedicated power amplifier driver in a radio frequency (RF) transmitter, in accordance with an embodiment of the invention. The communication device180may comprise an antenna182, a radio frequency (RF) receiver (Rx)184, a radio frequency (RF) transmitter (Tx)186, a processor188, a memory190, a DSP192, a display183, user controls185, a speaker187, and a microphone189.

The antenna182may be suitable for transmitting and/or receiving electromagnetic signals. Although a single antenna is illustrated, the invention is not so limited. In this regard, the RF Tx/Rx184may utilize a common antenna for transmission and reception of signals adhering to one or more wireless standards, may utilize different antennas for each supported wireless standard, and/or may utilize a plurality of antennas for each supported wireless standard.

The RF Rx184may comprise suitable logic circuitry and/or code that may be operable to receive data utilizing one or more wired, wireless, and/or optical standards. In various exemplary embodiments of the invention, the RF Rx184may be operable to communicate in adherence with cellular, WiMAX, Wi-Fi, Bluetooth, Zigbee, T1/E1, Ethernet, USB, IEEE 1394, analog audio standards, analog video standards, digital audio standards, and/or digital video standards. The radio RF Rx184may be operable to perform amplification, down-conversion, filtering, demodulation, and analog to digital conversion of received signals.

The RF Tx186may comprise suitable logic circuitry and/or code that may be operable to transmit data utilizing one or more wired, wireless, and/or optical standards. In various exemplary embodiments of the invention, the RF Tx186may be operable to communicate in adherence with cellular, WiMAX, Wi-Fi, Bluetooth, Zigbee, T1/E1, Ethernet, USB, IEEE 1394, analog audio standards, analog video standards, digital audio standards, and/or digital video standards. The radio RF Tx186may be operable to perform amplification, up-conversion, filtering, modulation, and digital to analog conversion of signals to be transmitted. In this regard, the RF Tx186may be operable to utilize a passive upconversion mixer to reduce chip area. The passive upconversion mixer may comprise metal-oxide-semiconductor field-effect transistor (MOSFET) switches. The MOSFET switches may be driven by analog local oscillator (LO) signals from a local oscillator. The operation of the passive upconversion mixer may be controlled by the received LO signals. A maximum gain may be achieved at the passive upconversion mixer by biasing the received analog LO signals. A MOS gate-to-source voltage Vgsmay be utilized to track MOS threshold voltage VTH. The MOS threshold voltage VTHtogether with a DC component of a received analog baseband signal, VBB—DC, may be utilized to retrieve a bias value of the received LO signal.

The processor188may comprise suitable logic, circuitry, and/or code that may enable processing data and/or controlling operations of the communication device180. In this regard, the processor188may be operable to provide control signals to the various other portions comprising the communication device180. The processor188may also control transfers of data between various portions of the communication device180. Additionally, the processor188may enable execution of applications programs and/or code for processing data and effectuating operation of the communication device180.

The memory190may comprise suitable logic, circuitry, and/or code that may enable storage or programming of information comprising parameters and/or code that may effectuate the operation of the communication device180. Stored information may comprise received data and/or data to be presented, transmitted, and/or otherwise processed. The parameters may comprise configuration data and the code may comprise operational code such as software and/or firmware, but the information need not be limited in this regard.

The display183may be operable to provide visual information to, and/or enable interaction by, a user of the communication device180. In various embodiments of the invention, a graphical user interface may be presented via the display183. In various embodiments of the invention, a visual media content such as video, images, and text may be presented via the display183.

The user controls185may be operable to enable user interaction with the communication device180to control services and/or content handled by the communication device180. The user controls185may comprise, for example, a keypad, a keyboard, a roller ball, a multidirectional button, a scroll wheels, and/or a touch screen.

The speaker187may be operable to present audio information to a user. The speaker may present voice from a phone call and/or music or ringtones played back by the cellular enabled communication device.

The microphone189may be operable to convert acoustic signals into electronic signals. The microphone may enable a user to participate in a phone call and/or interact with the cellular enabled communication device via oral input.

In an exemplary operation, the RF Tx186may be operable to process digital baseband data such as Bluetooth baseband data, and output to the processor188, the memory190, and/or the DSP192. The digital baseband data may be processed by the processor188, the memory190, and/or the DSP192to be transmitted to a target receiver. A passive upconversion mixer may be utilized within the RF Tx186to reduce chip area. Analog local oscillator (LO) signals may be received and used to drive the passive upconversion mixer. A maximum gain may be achieved at the passive upconversion mixer by biasing the received analog LO signals. A LO bias value may be retrieved by tracking MOS threshold voltage VTHof the passive upconversion mixer and DC component of the received analog baseband signals, VBB—DC.

FIG. 2is a diagram illustrating an exemplary radio frequency (RF) transmitter that utilizes a passive upconversion mixer, in accordance with an embodiment of the invention. Referring toFIG. 2, there is shown a radio frequency transmitter200comprising a transmitter RF front-end210, an antenna220, a baseband processor230, and a local oscillator (LO)240. The transmitter RF front-end210comprises a power amplifier (PA)212, a passive upconversion mixer214, a lowpass filter (LPF)216, and a digital-to-analog converter (DAC)218.

The transmitter RF front-end210may comprise suitable logic, circuitry, interfaces and/or code that may be operable to process outbound RF signals and transmit to a target receiver via the antenna220. The transmitter RF front-end210may enable conversion of digital baseband signals from the baseband processor230to corresponding RF signals to be amplified via the PA212for transmission.

The DAC218may comprise suitable logic, circuitry, interfaces and/or code that may be operable to convert received digital baseband signals from the baseband processor230to baseband analog signals. The baseband analog signals may be communicated with the LPF216for further processing.

The LPF216may comprise suitable logic, circuitry and/or code that may be operable to suppress intermediate frequency spurious on the output of the DAC218. The LPF216may be operable to reduce sideband components in the output of the DAC218. The output of the LPF216may be communicated to the passive upconversion mixer214.

The passive upconversion mixer214may comprise suitable logic, circuitry and/or code that may be operable to translate the resulted signals from the LPF216to radio frequency signals in conjunction with the local oscillator (LO)240. The passive upconversion mixer214may comprise a switching core. The switching core may comprise a pair of passive metal-oxide-semiconductor field-effect transistor (MOSFET) switches in order to reduce chip area. The pair of the passive MOSFET switches may be driven by using analog LO signals received from the LO240. The passive upconversion mixer214may be operable to achieve a maximum gain by biasing the received analog LO signals. A LO bias value may be determined by evaluating various aspects such as corresponding gate-to-source voltage threshold VTHand DC component of received analog baseband signal, VBB—DC, of the pair of the passive MOSFET switches. The radio frequency signals from the passive upconversion mixer214may be communicated with the power amplifier (PA)212using maximum gain from the passive upconversion mixer214.

The PA212may comprise suitable logic, circuitry and/or code that may be operable to amplify signals for transmission by using, for example, a Bluetooth protocol in 2.4 GHz. The PA212may be driven by the LPF216and/or the passive upconversion mixer214.

The antenna220may comprise suitable logic, circuitry and/or code that may be operable to receive and transmit signals in radio frequency (RF) bands. Although the single antenna220is illustrated inFIG. 2, the invention may not be so limited. Accordingly, one or more antennas may be utilized for receiving and/transmitting signals in radio frequency (RF) bands by the radio transceiver200without departing from the spirit and scope of various embodiments of the invention.

The baseband processor230may comprise suitable logic, circuitry and/or code that may be operable to process digitized baseband signals. The baseband processor230may be operable to perform such baseband operations as demodulation, decorrelation, decoding, and error correction. In the event that the digitized baseband signals may need to be transmitted by using, for example, a Bluetooth protocol in 2.4 GHz, the baseband processor230may be operable to communicate with the transmitter RF front-end210to transmit corresponding signals in radio frequency (RF) bands via the antenna220.

In an exemplary operation, in instances where the baseband processor230may need to transmit digitized baseband signals in a specific radio frequency band such as 2.4 GHz, the baseband processor230may communicate the digitized baseband signals with the DAC218. The DAC218may be operable to convert the received digitized baseband signals to corresponding baseband analog signals and communicate with the low pass filter (LPF)216. The LPF216may be operable to suppress sideband components in the received baseband analog signals and communicate to the passive upconversion mixer214. The passive upconversion mixer214may be operable to mix the received baseband analog signals with LO signals to convert the received baseband analog signals to radio frequency signals in the specific radio frequency band. The converted baseband analog signals may be communicated with the PA212using maximum gain from the passive upconversion mixer214. The converted baseband analog signals may be amplified at the PA212and communicated with the antenna220for transmission, accordingly.

FIG. 3is a diagram illustrating an exemplary switching core that is utilized in a passive upconversion mixer, in accordance with an embodiment of the invention. Referring toFIG. 3, there is shown a switching core300comprising a pair of MOSFET switches302and304. The MOSFET switch302comprises a pair of MOS transistor302aand302b. The MOSFET switch304comprises a pair of MOS transistor304aand304b. Gate voltages VLON(t)306and VLOP(t)308are two path local oscillator (LO) signals from the LO240, where t is time variable. Gate voltages VLON(t)306and VLOP(t)308may be expressed, for example, as followings:

Source voltages VSP(t)310aand VSN(t)310bare two voltages for baseband I and Q path signals input to the passive upconversion mixer214via the LPF216, where t is time variable. Exemplary expressions for source voltages VSP(t)310aand VSN(t)310bmay be represented as followings:

VSP⁡(t)=VBB_DC+AmPS⁢sin⁡(2⁢πTBB⁢t)VSN⁡(t)=VBB_DC-AmPS⁢sin⁡(2⁢πTBB⁢t)
where, VBB—DCis the DC components of baseband signals. AmPSis the amplitude of a source signal of, for example, the MOSFET switch302. TBBis an associated baseband (BB) cycle signal to the MOSFET switch302. Input voltage VIN(t)310is an input voltage of the switching core300. The input voltage VIN(t)310is expressed as VIN(t)=VSP(t)−VSN(t). The output voltages VOP(t)312aand VON(t)312bare two output voltage signals from the MOSFET switch302and the MOSFET switch304, respectively. Output voltage VOUT(t)314of the switching core300is expressed as VOUT(t)=VOP(t)−VON(t)=VIN(t)×f(t), where f(t)ε{−1,0,+1}316is a transfer function and is a pulse train function as illustrated inFIG. 3. Referring toFIG. 3, TON1and TON2are pulse durations for pulse value of 1 and −1 respectively.

In an exemplary operation, in the first half of the LO cycle of the output voltage VOUT(t)314, in instances when the MOSFET switch302ais ON, the MOSFET switch304ais OFF, the MOSFET switch302bis OFF and the MOSFET switch304bis ON, VOUT(t)=VOP(t)−VON(t)=(VSP(t)−VSN(t))(+1)=VIN(t)×(+1). In instances when the MOSFET switch302ais OFF, the MOSFET switch304ais OFF, the MOSFET switch302bis OFF and the MOSFET switch304bis OFF, VOUT(t)=VOP(t)−VON(t)=0=VIN(t)×(0). In the second of the half LO cycle of the output voltage VOUT(t)314, in instances when the MOSFET switch302ais OFF, the MOSFET switch304ais ON, the MOSFET switch302bis ON and the MOSFET switch304bis OFF, VOUT(t)=VOP(t)−VON(t)=(VSN(t)−VSP(t))(+1)=(VSP(t)−VSN(t))×(−1)=VIN(t)×(−1). In instances when the MOSFET switch302ais OFF, the MOSFET switch304ais OFF, the MOSFET switch302bis OFF and the MOSFET switch304bis OFF, VOUT(t)=VOP(t)−VON(t)=0=VIN(t)×(0).

FIG. 4is a diagram illustrating an exemplary MOS transistor circuit schematic, in accordance with an embodiment of the invention. Referring toFIG. 4, there is shown a MOS transistor400comprising a body (B) region402, a gate (G) terminal404, a drain (D) terminal406, and a source (S) terminal408.

The operation of the MOS transistor400may depend on various MOS transistor variables such as a gate voltage VG, a source voltage VS, and/or a MOS voltage threshold VTH. For example, the drain (D) terminal406is connected to the source (S) terminal408when VG−VS>VTH. The MOS transistor400may be turned ON. The drain (D) terminal406is disconnected to the source (S) terminal408when VG−VS≦VTH. The MOS transistor400may be turned OFF.

The operation of the MOS transistor400may vary depending on the voltage levels at associated terminals such as a gate voltage VGand/or a source voltage VSwith respect to MOS threshold voltage VTH. For example, when VG−VS≦VTH, the MOS transistor400may be turned OFF, and there is no conduction between the drain terminal406and the source terminal408. When VG−VS>VTH, the MOS transistor400is turned ON, and a channel has been created which allows current to flow between the drain terminal406and the source terminal408. The MOS transistor400may operate like a resistor, controlled by the gate voltage VGrelative to both a source voltage VSand a drain voltage VD. The body region402may be operated as a second gate, and is sometimes referred to as the “back gate”.

The performance of the MOS transistor400depends on the MOS threshold voltage VTH. However, the MOS threshold voltage VTHmay change substantially due to variation of, for example, the source to the body bias voltage VSB. The body bias voltage VSBis caused by body effects between the source terminal408and the body region402. The body effects may describe changes in the MOS threshold voltage VTHby the change in a baseband (BB) voltage VBBto the MOS transistor400. In this regard, the MOS transistor400may be operated to improve device performance by controlling the MOS threshold voltage Vthand/or dynamically adjusting the baseband (BB) voltage VBB.

FIG. 5is a diagram illustrating exemplary operation logic of a MOSFET switch when VLODC level is equal to VBB—DC+VTH, in accordance with an embodiment of the invention. Referring toFIG. 5, there is shown a signal VLOP(t)306and a signal VLON(t)308. As described with respect toFIG. 3, VOUT(t)=VOP(t)−VON(t)=VIN(t)×f(t), where f(t)ε{−1,0,+1}316is a transfer function which is a pulse train function as illustrated inFIG. 3. The switch core300may operate with a switch duty cycle Tswitch. The switch duty cycle Tswitch may be represented as

The switch duty cycle TSwitchmay be utilized as an indicator to a power level that the passive upconversion mixer214may provide for signal transmissions. A switch duty cycle TSwitchof 100% may correspond to the maximum gain that the passive upconversion mixer214may provide to communicate signals with the PA212.

The operation of the switching core300may be controlled by the received analog LO signals from the LO240. The received analog LO signals may comprise the signal VLOP(t)306and the signal VLON(t)308. The MOSFET switch302and the MOSFET switch304may be controlled by the signal VLOP(t)306and the signal VLON(t)308, respectively. In instances where by setting the DC level of the VLO(t) equal to VBB—DC+VTH, the pulse durations TON1and TON2of the pulse train314for the output voltage VOUT(t) may be

TON⁢⁢1=TLO2⁢⁢and⁢⁢TON⁢⁢2=TLO2.
The switch duty cycle may be

TSwitch=TON⁢⁢1+TON⁢⁢2TLO=100⁢%.
Accordingly, the maximum gain may be provided by the passive upconversion mixer214for signal transmission.

FIG. 6is a diagram illustrating exemplary operation logic of a MOSFET switch when VLODC level is set to be less than VBB—DC+VTH, in accordance with an embodiment of the invention. VOUT(t)=VOP(t)−VON(t)=VIN(t)×f(t), where f(t)ε{−1,0,+1}316is a transfer function which is a pulse train function with switch duty cycle defined as

TSwitch=TON⁢⁢1+TON⁢⁢2TLO.
Referring toFIG. 6, there is shown that in instances where the DC level of the VLOis set to be less than VBB—DC+VTH, the pulse durations TON1and TON2of the pulse train314for the output voltage VOUT(t) may be less than

TLO2.
The switch duty cycle may be

TSwitch=TON⁢⁢1+TON⁢⁢2TLO<100⁢%.
Accordingly, the power provided by the passive upconversion mixer214for signal transmission is below the maximum gain of the passive upconversion mixer214.

FIG. 7is a diagram illustrating exemplary operation logic of a MOSFET switch when VLO(t) DC level is set to be greater than VBB—DC+VTH, in accordance with an embodiment of the invention. Referring toFIG. 7, there is shown that in instances where a DC level of the VLO(t) is set to be greater than VBB—DC+VTH.

In the first half of the LO cycle of the output voltage VOUT(t)314, in instances when the MOSFET switch302ais ON, the MOSFET switch304ais OFF, the MOSFET switch302bis OFF and the MOSFET switch304bis ON, VOUT(t)=VOP(t)−VON(t)=(VSP(t)−VSN(t))(+1)=VIN(t)×(+1). In instances when the MOSFET switch302ais ON, the MOSFET switch304ais ON, the MOSFET switch302bis ON and the MOSFET switch304bis ON, VOUT(t)=VOP(t)−VON(t)=0=VIN(t)×(0). In instances when the MOSFET switch302ais OFF, the MOSFET switch304ais OFF, the MOSFET switch302bis OFF and the MOSFET switch304bis OFF, VOUT(t)=VOP(t)−VON(t)=0=VIN(t)×(0). In the second of the half LO cycle of the output voltage VOUT(t)314, in instances when the MOSFET switch302ais OFF, the MOSFET switch304ais ON, the MOSFET switch302bis ON and the MOSFET switch304bis OFF, VOUT(t)=VOP(t)−VON(t)=(VSN(t)−VSP(t))(+1)=(VSP(t)−VSN(t))×(−1)=VIN(t)×(−1). In instances when the MOSFET switch302ais ON, the MOSFET switch304ais ON, the MOSFET switch302bis ON and the MOSFET switch304bis ON, VOUT(t)=VOP(t)−VON(t)=0=VIN(t)×(0). In instances when the MOSFET switch302ais OFF, the MOSFET switch304ais OFF, the MOSFET switch302bis OFF and the MOSFET switch304bis OFF, VOUT(t)=VOP(t)−VON(t)=0=VIN(t)×(0). Accordingly, VOUT(t)=VOP(t)−VON(t)=VIN(t)×f(t), where f(t)ε{−1,0,+1}316is the transfer function which is a pulse train function as illustrated inFIG. 3.

FIG. 8is a flow chart illustrating exemplary operation logic of a MOSFET switch that is used in a passive upconversion mixer, in accordance with an embodiment of the invention. Referring toFIG. 8, the exemplary steps start with step802, analog local oscillator signals may be received by the MOSFET switch302from the LO240. In step804, a DC component VLO—DCof the received analog LO signal VLO(t), may be determined. In step806, a DC component VBB—DCof a received baseband signal VBB(t) may be determined. In step808, a MOS threshold voltage VTHof a MOSFET switch such as the MOSFET switch302may be determined based on, for example, device temperature and/or signal. In step810, it may be determined that if VLO—DCis equal to VBB—DC+VTH. In instances where VLO—DCis equal to VBB—DC+VTH, then in step814, where the passive upconversion mixer214may be operable to transmit received baseband signals using a maximum power. The exemplary steps may return to step802.

In step810, in instances where VLO—DCis not equal to VBB—DC+VTH, then in step812, where the DC component VLO—DCof the received analog LO signal VLO(T) may be set to VBB—DC+VTH. The exemplary steps continue in step814.

Aspects of a method and system for obtaining maximum gain of a passive upconversion mixer utilized in a transmitter are provided. In accordance with various embodiments of the invention, a passive upconversion mixer such as the passive upconversion mixer214may be utilized in the RF transmitter200for transmitting a signal at a frequency specified by, for example, a Bluetooth protocol. The passive upconversion mixer214may receive analog local oscillator (LO) signals from the local oscillator240. The passive upconversion mixer214comprises a pair of MOSFET switches such as the MOSFET switch302and the MOSFET switch304. The received analog LO signals may be utilized to control operation of the MOSFET switch302and/or the MOSFET switch304. For example, the MOSFET transistor302aand the MOSFET transistor302bof the MOSFET switch302may be turned ON or OFF based on, for example, the received analog LO signals. The passive upconversion mixer214may be operable to transmit signals with maximum gain of the passive upconversion mixer214. A MOS threshold voltage VTHmay be determined for the MOSFET switch302and the MOSFET switch304, respectively. The passive upconversion mixer214is operable to receive an analog baseband signal VBB(t) to the MOSFET switch302and/or the MOSFET switch304with the determined MOS threshold voltage VTH. A DC component VBB—DCof the received analog baseband signal VBB(t) may be determined for the MOSFET switch302and the MOSFET switch304, respectively. A DC component of the received analog LO signal, VLO—DC, may be compared with a combination, for example, a linear combination, of the determined VTHand the determined baseband DC component VBB—DC. The determined DC component of the received analog LO signal may be set to be equal to the combination of the determined MOS threshold voltage VTHand the DC component VBB—DCof the received analog baseband signal VBB(t) for the transmission of VBB(t) based on the comparison.