Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/06—Receivers
  • H04B1/16—Circuits
  • H04B1/1607—Supply circuits
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B15/00—Suppression or limitation of noise or interference
  • H04B15/02—Reducing interference from electric apparatus by means located at or near the interfering apparatus
  • H04B15/04—Reducing interference from electric apparatus by means located at or near the interfering apparatus the interference being caused by substantially sinusoidal oscillations, e.g. in a receiver or in a tape-recorder

Definitions

• the present invention relates generally to electronic devices employing a switched power supply. More particularly, the present invention relates to a noise management technique for a switched voltage supply.
• FIG. 1 is a block diagram of a prior art electronic device 100 using a switched power supply.
• the electronic device 100 includes a battery 102, a switch stimulus 104, a DC-to-DC converter 106 and operating circuits which, in the embodiment of FIG. 1, are transceiver circuits 108.
• the electronic device 100 forms part of a radiotelephone such as a cellular or personal communication system (PCS) telephone.
• PCS personal communication system
• the battery 102 is a depletable energy source which may be recharged and provides a substantially stable output voltage at a predetermined voltage value, such as 3.6 volts.
• the switch stimulus 104 provides a switching signal, such as a square wave at a predetermined frequency, labeled F switch in FIG. 1.
• the DC-to-DC converter 106 receives the battery voltage from the battery 102 and a switching signal from the switch stimulus 104 and produces an output voltage, labeled N output in FIG. 1. This output voltage may be stepped up in voltage value from the battery voltage or may be reduced in voltage value from the battery voltage.
• the output voltage is provided to the transceiver circuits 108 to serve as the operating supply voltage for the transceiver circuits 108.
• the DC-to-DC converter 106 may produce other output voltages in addition to V ou(put .
• the DC-to-DC converter implementation for a switched voltage supply is effective but has some disadvantages.
• the most notable disadvantage is the amount of noise generated by the switching operation of the DC-to-DC converter.
• the spectral noise generated by the DC- to-DC converter 106 is most apparent at the switching frequency and harmonics of the switching frequency.
• noise generated by the switching voltage supply follows Equation 1.
• a switching voltage supply with a switching frequency F switch of 540 kHz is used in a cellular telephone.
• the cellular telephone operates in a radiotelephone system having a receive band of 869.04 MHz to 893.97 MHz, with channel spacing of 30 kHz.
• the supply will generate noise components according to Equation (2).
• F noise m.540kHz (2)
• the spectral components of the switching noise fall within the receive band and may interfere with the overall operation of the receiver.
• certain harmonics corresponding to predetermined values of m in Equation (2) may cause spurious response within the transmitter.
• the locally generated switching stimulus is generally not controlled and is likely to vary over operating and environmental conditions of the cellular telephone. In some cases, it can vary as much as +/- 5%. This implies a further refinement to the definition for noise occurring in the electronic device 100 of FIG. 1 shown in Equation (3).
• a method and apparatus for accommodating noise in an electronic device comprises managing, rather than suppressing, the noise in the device.
• a noise signal produced at one or more noise frequencies is moved out of a frequency band of interest. This is done by shifting the frequencies of the noise signal to one or more shifted frequencies outside the frequency band of interest.
• the frequency of the generated noise signal is shifted above or below the specified receive band or transmit band for the radiotelephone.
• substantially all harmonics of the noise signal are shifted as well to ensure that the noise in the frequency band of interest is minimized.
• FIG. 1 is a block diagram of a prior art electronic device using a switched power supply
• FIG. 2 illustrates a noise spectrum for a switched power supply
• FIG. 3 is a block diagram of a radiotelephone operable in a radiotelephone system
• FIG. 4 is a block diagram of a portion of the radiotelephone of FIG. 3
• FIG. 5 is a block diagram of a second embodiment of a portion of the radiotelephone of FIG. 3.
• FIG. 3 is a block diagram of a radiotelephone system 300 including a mobile station or radiotelephone 302 and a base station 304.
• the base station 304 in the illustrated embodiment is one of a plurality of base stations in the system 300 configured for radio communication with mobile stations such as the radiotelephone 300 in a fixed geographic region surrounding the base station 304. Examples of such a system include cellular and personal communication systems as well as fixed and trunked radio systems. One particular example is North American Digital Cellular service according to J-STD-009, PCS IS-136 Based Mobile Station Minimum Performance 1900 MHz Standard and J-STD-010, PCS IS-136 Base Station Minimum Performance 1900 MHz Standard ("IS- 136").
• the base station 304 communicates radio frequency (RF) signals with the radiotelephone 302 to communicate data representative of voice and other data with the radiotelephone 302.
• RF radio frequency
• the radiotelephone 302 includes an antenna 306, a transceiver circuit 308, a controller 310, a memory 312, a clock circuit 314, a power control circuit 316, and a user interface 318.
• the transceiver circuit 308 includes a receiver 320, a transmitter 322, a synthesizer 324 and an oscillator 326.
• For receiving radio frequency signals from the base station 304 such signals are detected at the antenna 306 and converted to digital data in the receiver 320 by demodulating a received signal.
• the digital data are conveyed to the controller 310 for further processing.
• data are conveyed from the controller 310 to the transmitter 322.
• the transmitter modulates a carrier signal provided by the synthesizer 324.
• the modulated carrier is conveyed to the changement 306 for transmission of radio signals to the base station 304.
• the synthesizer 324 provides a carrier signal to the receiver 320 and the transmitter 322 for modulation and demodulation of radio signals. By varying the frequency of this carrier signal, the receiver 320 and the transmitter 322 may be tuned to different channels as required in the system 300.
• the synthesizer 324 may be configured in any conventional manner, for example, using a phase locked loop (PLL).
• the oscillator 326 is preferably a temperature compensated crystal oscillator (TCXO), stable to within +/- 2.5 ppm over all environmental and operating conditions, including humidity and aging. Any other highly stable source of a switching signal may be substituted.
• the controller 310 controls operation of the radiotelephone 302.
• the controller 310 is preferably implemented as a microcontroller, microprocessor or other digital logic device. As such, the controller 310 operates in conjunction with data and instructions stored in the memory 312. Timing of operations within the radiotelephone is controlled in response to clocking signals provided by the clock circuit 314.
• the power control circuit 316 preferably includes a battery or other depletable energy storage device, a DC-to-DC converter and other associated circuitry for forming a switched voltage supply.
• the power control circuit 316 provides operating voltages required for other circuits of the radiotelephone 302. For digital logic circuits, such as the controller 310, the operating voltages may be on the order of, for example, 1.5 or 1.8 volts.
• the operating voltages may be 5 volts or greater.
• the user interface 318 provides user control of the radiotelephone 302.
• the user interface 318 includes a keypad, a display, a microphone and a speaker.
• FIG. 4 is a block diagram showing a portion 400 of the radiotelephone 300 of FIG. 3 in accordance with the present embodiment.
• the radiotelephone portion 400 includes transceiver circuits 308, a battery 402, a DC-to-DC converter 404 and a temperature compensated crystal oscillator (TCXO) 406.
• the transceiver circuits 308 provide radio frequency communication with a remote radio such as a base station of a cellular or PCS radiotelephone system.
• the battery 402 provides operating power for the radiotelephone portion 400 and other circuits of the radiotelephone 300.
• the battery 402 provides a battery voltage at an output 410.
• the TCXO 406 is preferably an oscillator which provides a switching signal at an output 412, the switching signal having a very stable frequency over a wide range of conditions.
• the TCXO output signal is preferably stable within +/- 2.5 ppm over all environmental and operating conditions, including operating voltage, temperature, humidity and aging.
• the TCXO 406 uses a reference frequency of 19.44 MHz +/- 2.5 ppm.
• the switching signal provided by the oscillator 406 is used as both a switching stimulus for the DC-to-DC converter 404 and for providing the oscillator signal used by the transceiver circuits 308.
• the transceiver circuits 308 are responsive to the oscillator signal for modulating and demodulating RF signals.
• the transceiver 308 may include a synthesizer or other circuit for channel selection.
• the DC-to- DC converter forms a switched power supply responsive to the switching signal for providing operating power to circuits of the radiotelephone 300.
• the TCXO 406 forms a switch stimulus providing highly stable output signals including the oscillator signal and the switching signal.
• One or more frequency shifting circuits may be added in the path of the oscillator signal or the switching signal to adapt the frequencies of these signals to requirements of the circuits which receive them.
• the use of the TCXO advantageously improves the stability of the switching stimulus provided to the DC-to-DC converter to improve the predictability of the switching frequency ( ⁇ sw i tch ) of the switching signal provided to the DC-to-DC converter 404. This reduces the bandwidth of the noise produced by the switching signal. Further, this allows the oscillator used in conventional switching supplies to be removed.
• FIG. 5 is a block diagram of a portion 500 of the radiotelephone 302 of FIG. 3.
• the radiotelephone portion 500 includes transceiver circuits 308, a battery 402, a DC-to-DC converter 404 and a TCXO 406.
• the radiotelephone portion 500 includes a frequency shifting circuit 502.
• the battery 402 forms a direct current (DC) power source for powering the radiotelephone portion 500 and other circuits of the radiotelephone 302.
• the TCXO 406 forms a switch stimulus, providing a switching signal at an output 412. This switching signal is provided to the frequency shifting circuit 502 as well as to the transceiver circuit 308. Not all connections are shown in the drawing so as to not unduly complicate the drawing figures.
• the frequency of the switching signal is F switch .
• the DC-to-DC converter 404 produces an output DC voltage, labeled V output .
• the transceiver circuits 308 form operating circuitry responsive to the output
• the frequency shifting circuit 502 includes a multiplier 504 and a divider 506 in the illustrated embodiment.
• the multiplier 504 operates to increase the frequency of the switching circuit received from the TCXO 406.
• a divider 506 operates to divide down or reduce the frequency of the signal provided to the DC-to-DC converter 404.
• both the multiplier 504 and the divider 506 are programmable. That is, a multiply value (A) may be stored in the multiplier 504 to control the multiplication value applied by the multiplier 504. Similarly, a division value (B) may be stored in the divider 506 to control the frequency division value applied by the divider 506.
• the frequency shifting circuit includes control inputs 510 for receiving the clock signal, the programmable data values and a strobe signal. Preferably, these same signals are used for providing programmable data to the transceiver circuits 308.
• control inputs 510 for receiving the clock signal, the programmable data values and a strobe signal.
• these same signals are used for providing programmable data to the transceiver circuits 308.
• data may likewise be stored in the frequency shifting circuit 502 for controlling the frequency shift applied by the multiplier 504 and the divider 506.
• the multiplier 504 and the divider 506 provide two advantages.
• the divider 506 reduces the switching stimulus frequency that is presented to the DC-to-DC converter 404. This allows the DC-to-DC converter to be traditional in design.
• values of A and B may be chosen to shift the one or more frequencies of the noise signal to one or more shifted frequencies outside a frequency band of interest.
• the frequency band of interest includes a receive band and a transmit band as specified by the radiotelephone system.
• a cellular telephone in the United States has a receive band of 869.04 MHz to 893.97 MHz, with channel spacing of 30 kHz.
• a signal in the specific channel of interest can be processed.
• the channel of interest is defined by the radiotelephone system.
• the transceiver circuits 308 may then receive or transmit radio signals relatively free of interference from the noise produced by the switching power supply of the radiotelephone 302. After processing the signal, the frequency shift may be changed or removed so that the noise signal is returned to the original noise frequencies. This shifting of the noise frequencies can be done on a channel-by-channel basis. New values of A and/or B can be loaded with each new channel assignment. Thus, the switching frequency provided to the DC-to-DC converter 404 varies with channel selection. In a further enhancement, values of A and B can be chosen so that a guardband G of frequencies around the desired receiver frequency is unoccupied by the noise generated by the switching power supply. In this case, the controlling equation becomes
• F noise ⁇ (F ⁇ G/2) for (6) A conservative receiver noise guardband for narrowband cellular systems such as IS-136 may be on the order of +/- 8 channels or 480 kHz. Other guardband values may be chosen and variable guardband values may be selected as well.
• a and B may be chosen for controlling the multiplier 504 and the divider 506, respectively. In most systems, A cannot equal 1 for all cases.
• the switching frequency F swit l cannot be derived from integer division of the reference clock frequency
• the objective is to keep noise out of the guard band around the receive frequency Frx (i.e., the band of interest). Then:
• nB is an integer and this last equation is violated.
• A is not equal to 1
• the values of n, B and A can be chosen so as to guarantee nB/A is a non-integer.
• n equals 45. Since this number is odd, setting B to an odd value guarantees an odd numerator.
• guardband size determines the minimum frequency of the switching stimulus. For a switching frequency F switch ⁇ G, harmonic noise cannot be kept out of the guarded band.
• the switching frequency F switch (which is also the fundamental frequency of the noise) is equal to the reference frequency Fref times the multiplication value A and divided by the division value B.
• Frx/Fswitch is selected to be halfway between integer values. That is, if

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Transceivers (AREA)
• Mobile Radio Communication Systems (AREA)
• Noise Elimination (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=23987649

Family Applications (1)

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• 2000
  • 2000-12-27 CN CN 00808575 patent/CN1354910A/zh active Pending
  • 2000-12-27 EP EP00993830A patent/EP1228573A1/de not_active Withdrawn
  • 2000-12-27 AU AU2001229132A patent/AU2001229132A1/en not_active Abandoned
  • 2000-12-27 WO PCT/US2000/035276 patent/WO2001059944A2/en not_active Application Discontinuation

Non-Patent Citations (1)

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