RF band pass filter with feedback control

A wireless receiver comprises a band-pass filter module that includes an input for receiving a first pilot signal, an output that generates a first signal based on the first pilot signal, and a control input for adjusting a center frequency of the band-pass filter module. A control module determines the energy of the first signal, generates a control signal based on the energy, and communicates the control signal to the control input of the band-pass filter module.

FIELD OF THE INVENTION

The present invention relates to band-pass filters (BPFs) and more particularly to BPFs in wireless receivers.

BACKGROUND OF THE INVENTION

A wireless receiver includes an antenna system that receives a signal of interest as well as background noise and interference. The wireless receiver therefore includes a tuner having one or more BPFs to isolate the signal of interest.

When designing a BPF, ideally the bandwidth (BW) of the pass-band should be equal to the BW of the signal of interest. One challenge to achieving this goal is tuning the BPF so that the pass-band is centered at the carrier frequency (f0) of the signal of interest. If the pass-band is not centered, then the BPF introduces distortion to the signal of interest.

The challenge of centering the pass-band can be mitigated by increasing the BW of the BPF so that it is wider than the bandwidth of the signal of interest. However, increasing the BW of the BPF also increases the portion of undesirable signals that pass through it. These undesirable signals then reduce the linearity of the receiver. This distortion decreases the signal-to-noise ratio of the receiver and is at odds with the desire to maximize linearity of the receiver mode.

Referring now toFIG. 1, a radio-frequency (RF) tuner10of a receiver is shown. A signal Rx is received by an antenna system (not shown) and includes the signal of interest and the undesirable signals. The signal Rx is applied to an input of a first BPF12that rejects a substantial portion of the undesirable signals. An output of the first BPF12communicates with a low noise amplifier (LNA)14. The LNA14amplifies the signal and applies it to a second BPF16. The second BPF16generally has a narrower pass-band than the first BPF12. The second BPF16communicates the signal of interest to a mixer18. The mixer18receives a fixed-frequency signal from a local oscillator20and downconverts the frequency of the signal of interest. The mixer then provides the downconverted signal of interest to a baseband receiver22to be demodulated.

The linearity of the RF tuner10is dependent on the pass-bands of the first and second BPFs12,16being centered upon the signal of interest and having the smallest possible BWs.

Referring now toFIG. 2, a schematic diagram is shown of a simple BPF30. The received signal Rx is applied across a first parallel combination that includes a first inductor32and first adjustable capacitor34. One end of the first parallel combinations connected to a reference node, such as a ground40. The opposite end of the first parallel combination is connected to one end of a series combination that includes a second inductor44and a second adjustable capacitor46. The opposite end of the series combination is connected to one end of a second parallel combination that includes a second inductor50and a second adjustable capacitor52. The opposite end of the second parallel combination is connected to ground40. Each of the adjustable capacitors34,46, and52can be implemented with a varactor and an associated bias voltage.

The components of the BPF30are selected and adjusted to simultaneously pass the signal of interest to output terminals54and shunt as much of the undesirable signals to ground40. The effectiveness of the BPF30is affected by the accuracy of the capacitances of the first, second, and third adjustable capacitors34,46, and52, respectively. If their capacitances vary, such as may occur over time, temperature, and/or humidity, the center frequency (fc) of the BPF30will shift and its performance will deteriorate.

SUMMARY OF THE INVENTION

A wireless receiver comprises a band-pass filter module that includes an input for receiving a first pilot signal, an output that generates a first signal based on the first pilot signal, and a control input for adjusting a center frequency of the band-pass filter module. A control module determines the energy of the first signal, generates a control signal based on the energy, and communicates the control signal to the control input of the band-pass filter module.

In other features, a first local oscillator generates the first pilot signal. The band-pass filter receives a second pilot signal and generates a second signal based on the second pilot signal. The control module determines the energy of the second signal and bases the control signal on the energy of the second signal.

In still other features, a switch selectively connects a received signal to the input of the band-pass filter. The control module generates a switch signal for controlling the switch. The control module generates a switch signal for selectively operating the first local oscillator. A switch selectively connects a received signal to the input of the band-pass filter based on the switch signal.

In still other features, the first pilot signal is received via a wireless transmission. The wireless transmission includes a plurality of subcarrier frequencies. The control module varies the control signal until the energy of the first signal reaches a maximum value. The control module varies the control signal until the energy of the first signal and the energy of the second signal are equal.

In still other features, a sensor generates a sensor signal. The control module generates the control signal further based on the sensor signal. An amplifier receives the first signal and generates an amplified signal. A mixer receives the amplified signal, generates a third signal based on the amplified signal, and communicates the third signal to the control module. The control module determines the energy of the first signal based on the third signal. A demodulator receives the third signal and generates binary data based on the third signal. A media access controller (MAC) receives the binary data and generates data packets based on the binary data. A wireless transceiver includes a wireless transmitter and the wireless receiver.

In still other features, the wireless receiver is compliant with at least one of Institute of Electrical and Electronics Engineers (IEEE) standards 802.11, 802.11a, 802.11b, 802.11g, 802.11h, 802.11n, 802.16, 802.20, European Technical Standards Institute (ETSI) DVB-H, ETSI DVB-T, ETSI EN 300 401 V1.3.3, ETSI ES 201 980 V2.1.1, and National Radio Standards Committee (NRSC)-5.

In other features, a wireless receiver comprises band-pass filtering means for filtering and including input means for receiving a first pilot signal, output means for generating a first signal based on the first pilot signal, and center frequency adjusting means for adjusting a center frequency of the band-pass filtering means. The wireless receiver further includes control means for determining the energy of the first signal, for generating a control signal based on the energy, and for communicating the control signal to the center frequency adjusting means of the band-pass filtering means.

In still other features, the wireless receiver comprises first local oscillating means for generating the first pilot signal. The band-pass filtering means receives a second pilot signal and generates a second signal based on the second pilot signal. The control means determines the energy of the second signal and bases the control signal on the energy of the second signal.

In still other features, the wireless receiver comprises switching means for selectively connecting a received signal to the input means of the band-pass filtering means. The control means generates a switch signal for controlling the switching means. The control means generates a switch signal for selectively operating the first local oscillating means. The wireless receiver comprises switching means for selectively connecting a received signal to the input means of the band-pass filtering means based on the switch signal.

In still other features, the first pilot signal is received via a wireless transmission. The wireless transmission includes a plurality of subcarrier frequencies. The control means varies the control signal until the energy of the first signal reaches a maximum value. The control means varies the control signal until the energy of the first signal and the energy of the second signal are equal.

In still other features, the wireless receiver comprises sensor means for generating a sensor signal. The control means generates the control signal further based on the sensor signal. The wireless receiver comprises amplifying means for receiving the first signal and generating an amplified signal. The wireless receiver comprises mixing means for receiving the amplified signal, generating a third signal based on the amplified signal, and communicating the third signal to the control means. The control means determines the energy of the first signal based on the third signal.

In still other features, the wireless receiver comprises demodulating means for receiving the third signal and generating binary data based on the third signal. The wireless receiver comprises media access control means for receiving the binary data and generating data packets based on the binary data. A wireless transceiver includes wireless transmitting means for transmitting wireless signals and the wireless receiver.

In still other features, the wireless receiver is compliant with at least one of Institute of Electrical and Electronics Engineers (IEEE) standards 802.11, 802.11a, 802.11b, 802.11g, 802.11h, 802.11n, 802.16, 802.20, European Technical Standards Institute (ETSI) DVB-H, ETSI DVB-T, ETSI EN 300 401 V1.3.3, ETSI ES 201 980 V2.1.1, and National Radio Standards Committee (NRSC)-5.

In other features, a method for receiving wireless signals comprises providing a band-pass filter module that includes an input, an output, and a control input. A first pilot signal is received at the input. A first signal is generated at the output based on the first pilot signal. A center frequency of the band-pass filter module is adjusted at the control input. The energy of the first signal is determined. A control signal is generated based on the energy. The control signal is communicated to the control input.

In still other features, the first pilot signal is generated at a first local oscillator. A second pilot signal is received. A second signal is generated based on the second pilot signal. The energy of the second signal is determined. The control signal is based on the energy of the second signal. A received signal is selectively connected to the input of the band-pass filter.

In still other features, a switch signal for selectively connecting the received signal to the input of the band-pass filter is generated. A switch signal for selectively operating the first local oscillator is generated. A received signal is selectively connected to the input of the band-pass filter based on the switch signal.

In still other features, the first pilot signal is received via a wireless transmission. The wireless transmission includes a plurality of subcarrier frequencies. The control signal is varied until the energy of the first signal reaches a maximum value. The control signal is varied until the energy of the first signal and the energy of the second signal are equal.

In still other features, a sensor signal is generated. The control signal is generated based on the sensor signal. The first signal is received and an amplified signal is generated in response to the first signal. The amplified signal is received. A third signal is generated based on the amplified signal. The energy of the first signal is determined based on the third signal. The third signal is received. Binary data is generated based on the third signal. The binary data is received. Data packets are generated based on the binary data. A wireless transceiver implements the method for receiving wireless signals. A wireless receiver implements the method for receiving wireless signals. The method is compliant with at least one of Institute of Electrical and Electronics Engineers (IEEE) standards 802.11, 802.11a, 802.11b, 802.11g, 802.11h, 802.11n, 802.16, 802.20, European Technical Standards Institute (ETSI) DVB-H, ETSI DVB-T, ETSI EN 300 401 V1.3.3, ETSI ES 201 980 V2.1.1, and National Radio Standards Committee (NRSC)-5.

In other features, a computer program executed by a processor comprises receiving a first pilot signal at an input of a band-pass filter module. A first signal is generated at an output of the band-pass filter module based on the first pilot signal. A center frequency of the band-pass filter module is adjusted. The energy of the first signal is adjusted. A control signal is generated based on the energy. The control signal is communicated to the band-pass filter module.

In still other features, a second pilot signal is received. A second signal is generated based on the second pilot signal. The energy of the second signal is determined. The control signal is based on the energy of the second signal. A received signal is selectively connected to the input of the band-pass filter.

In still other features, a switch signal for selectively connecting the received signal to the input of the band-pass filter is generated. A switch signal is generated for selectively operating a first local oscillator that generates the first pilot signal. A received signal is selectively connected to the input of the band-pass filter based on the switch signal.

In still other features, the first pilot signal is received via a wireless transmission. The wireless transmission includes a plurality of subcarrier frequencies. The control signal is varied until the energy of the first signal reaches a maximum value. The control signal is varied until the energy of the first signal and the energy of the second signal are equal.

In still other features, a sensor signal is generated. The control signal is generated based on the sensor signal. The first signal is received and an amplified signal is generated in response to the first signal. The amplified signal is received. A third signal is generated based on the amplified signal. The energy of the first signal is determined based on the third signal. The third signal is received. Binary data is generated based on the third signal. The binary data is received. Data packets are generated based on the binary data. A wireless transceiver implements the computer program. A wireless receiver implements the computer program.

The computer program is compliant with at least one of Institute of Electrical and Electronics Engineers (IEEE) standards 802.11, 802.11a, 802.11b, 802.11g, 802.11h, 802.11n, 802.16, 802.20, European Technical Standards Institute (ETSI) DVB-H, ETSI DVB-T, ETSI EN 300 401 V1.3.3, ETSI ES 201 980 V2.1.1, and National Radio Standards Committee (NRSC)-5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 3, a functional block diagram is shown of an improved RF tuner100and baseband processor102. The RF tuner100and baseband processor102can be implemented to be compatible with the Institute of Electrical and Electronics Engineers (IEEE) standards 802.11, 802.11a, 802.11b, 802.11g, 802.11h, 802.11n, 802.16, and/or 802.20. The RF tuner100and baseband processor102can also be implemented to be compatible with European Telecommunications Standard Institute (ETSI) Digital Video Broadcasting (DVB), Digital Audio Broadcasting (DAB), and Digital Radio Mondiale (DRM) standards, which are hereby incorporated by reference in their entirety. The RF tuner100and baseband processor102can also be implemented to be compatible with the National Radio Systems Committee (NRSC) In-band/On-channel Digital Radio Broadcasting Standard, NRSC-5, which is hereby incorporated by reference in its entirety.

The RF tuner100receives a signal Rxfrom an antenna system (not shown). The signal Rxincludes a signal of interest and undesirable signals such as noise and interference. The signal Rx is applied to a switch104that selectively communicates the signal Rx to a first band-pass filter (BPF)106. The first BPF106reduces the energy of the undesirable signals and communicates the filtered Rx signal to a low-noise amplifier (LNA)108. The LNA108amplifies the filtered Rx signal and communicates it to a second BPF110. The second BPF110has a bandwidth (BW) that is equal to or narrower than the first BPF106. The second BPF110reduces the energy of the remaining undesirable signals and communicates a signal, which is now primarily comprised of the signal of interest, to a mixer112. In some embodiments the second BPF110is omitted, in which case the output of the LNA108is applied to the input of the mixer112. The mixer112also receives a signal from a first local oscillator114and downconverts the carrier frequency (f0) of the signal of interest before communicating it to the baseband processor102.

The RF tuner100receives a center control signal116that adjusts the center-frequency (fc) of the first BPF106and second BPF110. The baseband processor102generates the center control signal116in accordance with a method that is described later and used to periodically align fcwith f0.

The RF tuner100also receives a pilot control signal120that selectively activates a pilot signal generator122and opens the switch104. In some embodiments, the pilot signal generator122generates a pilot signal124having the frequency f0. In other embodiments, the pilot signal generator122generates a lower frequency (f0−Δ) and an upper frequency (f0+Δ), where Δ is a fixed frequency. The frequencies f0−Δ and f0+Δ should be selected so that they are within the pass-bands of both the first and second BPFs106,110.

The pilot signal124is communicated to the input of the first BPF106and continues to propagate through the LNA108, second BPF110, and the mixer112. The baseband processor102receives the pilot signal from the mixer112and measures the remaining pilot signal energy. The baseband processor102then uses the measured energy to adjust the center control signal116as described below.

The baseband processor102will now be described in additional detail. A modem150receives the signal from the mixer112. The signal is applied to an analog-to-digital converter (ADC)152. The ADC152converts the signal to a binary format and communicates it to a control/interface module156. The control/interface module156parses the binary signal for data and to determine the energy of the signal that the ADC152received. The control/interface module156communicates the data to a media access control module (MAC)160. The MAC160formats the data into packets and communicates it to a host module164via an interface module162. The host module164can include at least one of a number of digital appliances and/or computing devices that are described later herein. The control/interface module156can also receive a sensor signal158from a sensor159. The sensor159can include a temperature sensor, a clock, etc. The control/interface module156generates the center control signal116and the pilot control signal120in accordance with methods that are described later herein.

Referring now toFIGS. 4A and 4B, plots are shown that indicate the relationship between fcand the energy of the pilot signal124having a single frequency f0. An unscaled vertical axis202represents gain (A) and an unscaled horizontal axis204represents frequency (f). A curve206represents the combined pass-band of the first BPF106and/or the second BPF110. A vertical arrow208represents the pilot signal as measured by the baseband processor102. The length of the vertical arrow208indicates the magnitude of the energy.

InFIG. 4A, the length of the vertical arrow208is at a maximum, which indicates fcis aligned with f0. When fcis misaligned with f0, then the pilot signal energy will decrease from the maximum. Such a condition is shown inFIG. 4B. The baseband processor102can therefore monitor the pilot signal energy while it adjusts fcvia the center control signal116. When the pilot signal energy reaches its maximum value, the baseband processor102can hold the center control signal116constant to keep fcaligned with f0.

Referring now toFIGS. 5A and 5B, plots are shown that indicate the relationship between fcand the energy of the pilot signal124that has two frequencies, f0−Δ and f0+Δ. A first vertical arrow210represents the pilot signal at frequency f0−Δ. A second vertical arrow212represents the pilot signal at frequency f0+Δ. The pilot signals are measured by the baseband processor102. The lengths of the first and second vertical arrows210,212indicate the magnitude of their respective energies.

InFIG. 5A, the lengths of the first vertical arrow210and the second vertical arrow212are equal. Since f0−Δ and f0+Δ are centered about f0, the equal lengths of the arrows indicate that fcis aligned with f0. When fcis misaligned with f0, then the pilot signal energies will differ between f0−Δ and f0+Δ. Such a condition is shown inFIG. 5B. The baseband processor102can therefore monitor the difference between the pilot signal energies at f0−Δ and f0+Δwhile it adjusts fc. The baseband processor102can also use the polarity and magnitude of the difference, as exemplified by a dashed line207, to determine which direction and amount to adjust fc.

Referring now toFIGS. 6 and 7, first and second methods300and350are respectively shown for adjusting fc. The method300(FIG. 6) is suitable for use with the single frequency pilot signal as described above inFIGS. 4A and 4B. The method350(FIG. 7) is suitable for use with the pilot signal having lower and upper frequencies as described above inFIGS. 5A and 5B. The methods300and350can be stored as computer programs in the baseband processor102and executed as needed to align fcwith f0. In some applications, the selected method is executed only at power-up. In other applications, the selected method is executed when the sensor signal130exceeds a sensor signal threshold. In yet other applications, the selected method is executed periodically. In cases where the signal of interest is a burst-type signal, the selected method can be executed during quiet periods between each burst. Examples of burst-type signals include signals such as those used in the Institute of Electrical and Electronics Engineers (IEEE) 802.11a, 802.11g, and 802.11n protocols and the European Technical Standards Institute (ETSI) DVB-H protocol.

Referring now toFIG. 6, the first method300will be described in more detail. Control begins in block302and proceeds to block304. In block304, control uses the pilot control signal120to selectively generate the pilot signal124. Control then proceeds to decision block306and determines whether the pilot signal energy passing through the first BPF106and/or the second BPF110is at a maximum. If the pilot signal energy is not at the maximum, then control proceeds to block308and uses the center control signal116to adjust fc. Control then returns to decision block306and determines whether the pilot signal energy is at a maximum with the recently-adjusted fc. Control continues to loop through blocks306and308until maximum amount of pilot signal energy is determined in decision block306, at which control proceeds to block310and turns the pilot signal124off. Control then exits through block312.

Referring now toFIG. 7, the second method350will be described in more detail. Control enters through block352and proceeds to block354. In block354, control generates the pilot signal124at the lower frequency f0−Δ. Control then proceeds to block354and measures the pilot signal energy at the lower frequency f0−Δ. Control then proceeds to block358and generates the pilot signal124at the upper frequency f0+Δ. Control then proceeds to block360and measures the pilot signal energy at the upper frequency f0+Δ. Control then proceeds to decision block362and determines the difference between the pilot signal energies at the lower frequency f0−Δ and the upper frequency f0+Δ. If the difference is nonzero, then control branches to block366and uses the center control signal116to adjust fc. The degree and direction that fcis adjusted can be based on the magnitude and/or polarity of the difference determined in decision block362. Control then returns to block354from block366again generates the pilot signal124at the lower frequency f0−Δ and the upper frequency f0+Δ. Control continues to loop through blocks354-366until the difference between the pilot signal energies is zero in decision block362, at which point control proceeds to block368and turns the pilot signal124off. Control then exits through block370.

Referring now toFIGS. 8A-8E, various exemplary implementations of the present invention are shown. Referring now toFIG. 8A, the present invention can be implemented in a high definition television (HDTV)420. The present invention may implement a WLAN interface of the HDTV420. The HDTV420receives HDTV input signals in either a wired or wireless format and generates HDTV output signals for a display426. In some implementations, signal processing circuit and/or control circuit422and/or other circuits (not shown) of the HDTV420may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other type of HDTV processing that may be required.

The HDTV420may communicate with mass data storage427that stores data in a nonvolatile manner such as optical and/or magnetic storage devices. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The HDTV420may be connected to memory428such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The HDTV420also may support connections with a WLAN via a WLAN network interface429.

Referring now toFIG. 8B, the present invention implements a WLAN interface of a vehicle control system. In some implementations, the present invention implement a powertrain control system432that receives inputs from one or more sensors such as temperature sensors, pressure sensors, rotational sensors, airflow sensors and/or any other suitable sensors and/or that generates one or more output control signals such as engine operating parameters, transmission operating parameters, and/or other control signals.

The present invention may also be implemented in other control systems440of the vehicle430. The control system440may likewise receive signals from input sensors442and/or output control signals to one or more output devices444. In some implementations, the control system440may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated.

The powertrain control system432may communicate with mass data storage446that stores data in a nonvolatile manner. The mass data storage446may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The powertrain control system432may be connected to memory447such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The powertrain control system432also may support connections with a WLAN via a WLAN network interface448. The control system440may also include mass data storage, memory and/or a WLAN interface (all not shown).

Referring now toFIG. 8C, the present invention can be implemented in a cellular phone450that may include a cellular antenna451. The present invention may implement a WLAN interface of the cellular phone450. In some implementations, the cellular phone450includes a microphone456, an audio output458such as a speaker and/or audio output jack, a display460and/or an input device462such as a keypad, pointing device, voice actuation and/or other input device. The signal processing and/or control circuits452and/or other circuits (not shown) in the cellular phone450may process data, perform coding and/or encryption, perform calculations, format data and/or perform other cellular phone functions.

The cellular phone450may communicate with mass data storage464that stores data in a nonvolatile manner such as optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The cellular phone450may be connected to memory466such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The cellular phone450also may support connections with a WLAN via a WLAN network interface468.

Referring now toFIG. 8D, the present invention can be implemented in a set top box480. The present invention may implement a WLAN interface of the set top box480. The set top box480receives signals from a source such as a broadband source and outputs standard and/or high definition audio/video signals suitable for a display488such as a television and/or monitor and/or other video and/or audio output devices. The signal processing and/or control circuits484and/or other circuits (not shown) of the set top box480may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other set top box function.

The set top box480may communicate with mass data storage490that stores data in a nonvolatile manner. The mass data storage490may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The set top box480may be connected to memory494such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The set top box480also may support connections with a WLAN via a WLAN network interface496.

Referring now toFIG. 8E, the present invention can be implemented in a media player500. The present invention may implement a WLAN interface of the media player500. In some implementations, the media player500includes a display507and/or a user input508such as a keypad, touchpad and the like. In some implementations, the media player500may employ a graphical user interface (GUI) that typically employs menus, drop down menus, icons and/or a point-and-click interface via the display507and/or user input508. The media player500further includes an audio output509such as a speaker and/or audio output jack. The signal processing and/or control circuits504and/or other circuits (not shown) of the media player500may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other media player function.

The media player500may communicate with mass data storage510that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. The mass data storage may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The media player500may be connected to memory514such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The media player500also may support connections with a WLAN via a WLAN network interface516. Still other implementations in addition to those described above are contemplated.