WO1999056401A1 - Circuit for reduction of cross modulation and increased battery life in a battery powered transceiver - Google Patents
Circuit for reduction of cross modulation and increased battery life in a battery powered transceiver Download PDFInfo
- Publication number
- WO1999056401A1 WO1999056401A1 PCT/US1999/008883 US9908883W WO9956401A1 WO 1999056401 A1 WO1999056401 A1 WO 1999056401A1 US 9908883 W US9908883 W US 9908883W WO 9956401 A1 WO9956401 A1 WO 9956401A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- transmitting
- resister
- bias current
- transmitter
- amplifier
- Prior art date
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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
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/109—Means associated with receiver for limiting or suppressing noise or interference by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
Definitions
- This invention relates to battery powered radios and is of particular advantage for reducing cross modulation in battery powered full duplex radio telephone transceivers.
- the primary contributor to cross modulation distortion in the receiver section of a radio telephone is the transmitter of the same radio telephone.
- a full-duplex radio telephone is capable of transmitting and receiving at the same time. Because radio telephones are so small, the transmitter and the receiver are of necessity located very close to each other. It is unavoidable that energy, particularly high power level energy, transmitted by the radio telephone will leak into, and cause distortion of signals received by, the receiver portion of the radio telephone. In particular, the distortion will find its way to the input of the receiver section low noise amplifier (LNA) and the distortion will be amplified and will corrupt the desirable signals and information received by the receiver.
- LNA low noise amplifier
- a portable radio telephone 20 using CDMA (code division multiple access) technology may be located a relatively great distance D from its CDMA compatible base station (BTS) 10 and may at the same time be significantly closer (distance d) to a base station 30 of a competing non-CDMA technology.
- the CDMA base station 10, phone 20 and competing technology base station 30 each transmit at their respective frequencies fl, f2 and f3 via respective antennas 12, 22 and 32. Because the telephone 20 is relatively far from its base station 10 the signal transmitted by the CDMA base station will be very weak when received by the telephone.
- the phone 20 will detect this weak signal level and determine that in order to communicate with the base station 10 the phone will have to transmit (at f2) at a relatively high power. Due to the phone's proximity to the competing technology base station 30, the signal transmitted (at f3) by the competing technology base station will be received by the phone 20 at a relatively high power level. These two high power signals will cross modulate and generate distortion of relatively high power at frequencies that are within the frequency range of the receiver section of the phone. To illustrate, f2 which may be 1908.75 MHz, and f3 which may be 1987.5 MHz, will cross modulate to produce distortion at frequencies which lie within the frequency range 1985 MHz to 1990 MHz of the receiver portion of phone 20. This will produce unwanted distortion of the desirable received information as it is processed in the low noise amplifier of the phone 20.
- the bias point (quiescent point) can be selected according to the expected operating conditions.
- Gonzalez suggests different fixed quiescent operating points depending on the anticipated operating conditions. For example, a first point (point A) is recommended for low noise and low power amplification.
- a second point (point B), reflecting a higher bias current, is recommended for operation at low noise and higher power gain.
- This second condition (point B) is substantially the situation illustrated in FIG. 1, i.e. a high power intercept point is required.
- the present invention provides a means for increasing the bias current of a LNA in the receiver portion of a transceiver when the transmitter portion of the transceiver is transmitting, and returning the bias current to a lower operating level when the transmitter is not transmitting.
- the level of the increased bias current is chosen such that the LNA operates in a highly linear fashion, thereby minimizing cross modulation, even in the presence of high transmit power.
- a trigger signal is chosen that is representative of the state of the transmitter, i.e. it indicates when the transmitter is transmitting and when it is not. When the transmitter is transmitting, the trigger signal activates a switch which places a resister in parallel with a resister that sets the bias current for the LNA.
- the effective resistance is thus lowered, which increases the bias current.
- the trigger signal may be integrated before it is provided to the switch.
- FIG. 1 illustrates the circumstance when cross modulation poses a severe problem for a portable radio telephone.
- FIG. 2 is a circuit schematic of a Low Noise Amplifier illustrating implementation of a preferred embodiment of the invention.
- FIG. 3 is a schematic of an alternate switching circuit for adjusting the bias current provided to the Low Noise Amplifier.
- the transmit circuitry and the receiver Low Noise Amplifier are, of necessity, located proximate one another. This proximity causes unwanted cross modulation distortion.
- the high power energy emitted by the transmitter cross modulates with power from a nearby competing base station (sometimes called a "jammer") and couples into the LNA and is amplified, thus interfering with and degrading the quality of the received signal which is also amplified by the receiver LNA.
- a nearby competing base station sometimes called a "jammer”
- FIG. 2 A simplified circuit schematic diagram of a LNA, showing implementation of an embodiment of the invention in the form of bias switching circuit 70, is shown in FIG. 2.
- the LNA consists of a first stage LNA 50 and its associated bias circuit 52, a second stage LNA 56 and its associated bias circuit 58 and a mixer /downconverter 60 including a Local Oscillator (LO) 62 coupled to the output of the second stage LNA.
- the first stage LNA is connected to the second stage LNA through a filter 54 which is configured to pass signals in the receiver frequency range and to reject signals in the transmitter frequency range.
- the second stage LNA and its bias circuit are substantially similar to the first stage LNA and its bias circuit and therefore the details of the second stage LNA and its bias circuit are not shown. This allows for simplification of FIG. 2.
- Previous design approaches for reducing cross modulation distortion configured the bias circuit to set the bias current of Ql to a level which ensured satisfactory (i.e. linear) operation even in the most challenging conditions which occur when the transmitter is transmitting at high power. This resulted in the first stage LNA being continuously biased at a relatively high current level. The resultant drain on the transceiver battery significantly shortens battery life, reducing standby time and talk time. These previous design approaches resulted in selection of a fixed bias point which produced a continuous and relatively high current drain. In contrast, the approach of the present invention is to configure the bias circuit to provide as low a bias current as possible (i.e.
- FIG. 2 shows a low noise amplifier located within the receiver portion of a battery powered transceiver.
- the first stage LNA 50 of LNA 40 comprises a transistor Ql.
- the bias current for Ql is established by the bias circuit 52 and in particular by the values of R15 and Rll.
- Prior art LNA designs resulted in relatively low values for Rll in order to generate relatively high bias current. (As used in this description "relatively” refers to a comparison between values typical of the prior art and those values which result from implementation of the invention.)
- the output of the first stage LNA 50 is passed through a filter 54 which passes signals having a frequency within the receiver frequency range and rejects signals having a frequency within the frequency range of the transmitter portion of phone 20.
- the output of the filter 54 is input to the second stage LNA 56 and output to a mixer/downconverter 60.
- the resulting intermediate frequency (IF) signal RX_IF is further processed by other circuitry (not shown) within the transceiver.
- the present invention provides means for detecting the on/ off state of the transmitter of the radio telephone transceiver 20 and for increasing the bias current of the first stage LNA 50 only during the time that the transmitter is transmitting.
- An embodiment of the invention as illustrated in FIG. 2 uses a trigger signal (MSM_PA_ON) which provides a suitably reliable indication of the state of the transmitter.
- MSM_PA_ON a trigger signal which provides a suitably reliable indication of the state of the transmitter.
- the trigger signal must consistently indicate a first state whenever the transmitter is transmitting, and must consistently indicate a second state (different from the first state) whenever the transmitter is not transmitting.
- the selected trigger signal was a digital signal, and one state was indicated by the voltage exceeding about 1.65 volts and the other state was indicated by the voltage being less than 1.65 volts.
- the bias switching circuit 70 comprises a transistor Q25 having an input port (its base) for receiving the trigger signal, a switching field effect transistor (FET) Q24 and resister R12.
- the collector of transistor Q25 is coupled to the gate of FET Q24.
- the source of FET Q24 is connected to one terminal of Rll and the drain of FET Q24 is connected to one terminal of R12.
- the other terminal of R12 is connected to the other terminal of Rll.
- FET Q24 is connected in series with resister R12, and FET Q24 and R12 together are connected in parallel with Rll.
- the transistor Q25 turns on and activates switching FET Q24 which closes and thereby connects resister R12 in parallel with resister Rll.
- the specific values of the circuit elements such as Rll and R12 are chosen so that the bias current is raised to a level which insures satisfactory (i.e. highly linear) operation of the first stage LNA 50 during the time that the transmitter is transmitting. This results in reduced cross modulation distortion. Since the bias current is only increased when the transmitter is transmitting, use of this bias switching circuit also results in decreased current drain from the transceiver battery. This in turn produces longer standby time and longer talk time.
- the bias current can be switched between two desired values by the use of any functionally equivalent circuit.
- Oner such functionally equivalent circuit is the circuit shown in Fig. 3.
- the switch (Q24) is connected in parallel across one of the resisters, e.g. Ra. When Q24 is triggered "on” it shorts Ra, reducing the effective resistance from Ra + Rb to Rb, thereby increasing the bias current provided to Ql.
- the actual values of Ra and Rb would be chosen to achieve the two different bias currents, e.g. 10 mA and 20 mA.
- Various other such equivalent circuits could readily be devised.
- the transmitter will turn on and off rapidly, i.e. at a frequency of about 50 Hz or more. If the bias current to the first stage LNA (Ql) is allowed to change at the same frequency or higher, undesirable transient effects will occur.
- Q25 may be operated as an integrator circuit.
- R10, CH and Q25 are configured as an integrator, having a time constant of about 0.47 seconds, to smooth out the trigger signal and hold Q24 on (i.e. in the closed state) if the trigger signal is pulsating at a frequency of about 10 Hz or higher. At lower frequencies, the pulsating trigger signal will be allowed to cause the switching FET Q24 to also turn on and off at the same pulsating rate.
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Transceivers (AREA)
- Transmitters (AREA)
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99919986A EP1080535A1 (en) | 1998-04-24 | 1999-04-23 | Circuit for reduction of cross modulation and increased battery life in a battery powered transceiver |
AU37580/99A AU3758099A (en) | 1998-04-24 | 1999-04-23 | Circuit for reduction of cross modulation and increased battery life in a battery powered transceiver |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US6607098A | 1998-04-24 | 1998-04-24 | |
US09/066,070 | 1998-04-24 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999056401A1 true WO1999056401A1 (en) | 1999-11-04 |
Family
ID=22067061
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/008883 WO1999056401A1 (en) | 1998-04-24 | 1999-04-23 | Circuit for reduction of cross modulation and increased battery life in a battery powered transceiver |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP1080535A1 (en) |
AU (1) | AU3758099A (en) |
WO (1) | WO1999056401A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0987825A1 (en) * | 1998-03-20 | 2000-03-22 | Kabushiki Kaisha Toshiba | Radio transmitter/receiver, high-frequency radio receiver, and control unit |
WO2001076082A2 (en) * | 2000-03-31 | 2001-10-11 | Siemens Aktiengesellschaft | Mobile radio device and a method for receiving an hf signal |
WO2004004144A1 (en) * | 2002-06-28 | 2004-01-08 | Qualcomm Incorporated | Blind cancellation of cross-modulation by addition of modulated signal |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5483190A (en) * | 1994-12-01 | 1996-01-09 | United Technologies Corporation | Floating voltage controlled thermistor/platinum probe emulator |
US5815821A (en) * | 1994-01-12 | 1998-09-29 | Telefonaktiebolaget Lm Ericsson | Method and a device for conserving power in a battery powered transceiver |
-
1999
- 1999-04-23 EP EP99919986A patent/EP1080535A1/en not_active Withdrawn
- 1999-04-23 WO PCT/US1999/008883 patent/WO1999056401A1/en not_active Application Discontinuation
- 1999-04-23 AU AU37580/99A patent/AU3758099A/en not_active Abandoned
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5815821A (en) * | 1994-01-12 | 1998-09-29 | Telefonaktiebolaget Lm Ericsson | Method and a device for conserving power in a battery powered transceiver |
US5483190A (en) * | 1994-12-01 | 1996-01-09 | United Technologies Corporation | Floating voltage controlled thermistor/platinum probe emulator |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0987825A1 (en) * | 1998-03-20 | 2000-03-22 | Kabushiki Kaisha Toshiba | Radio transmitter/receiver, high-frequency radio receiver, and control unit |
EP0987825A4 (en) * | 1998-03-20 | 2004-12-08 | Toshiba Kk | Radio transmitter/receiver, high-frequency radio receiver, and control unit |
WO2001076082A2 (en) * | 2000-03-31 | 2001-10-11 | Siemens Aktiengesellschaft | Mobile radio device and a method for receiving an hf signal |
WO2001076082A3 (en) * | 2000-03-31 | 2002-02-07 | Siemens Ag | Mobile radio device and a method for receiving an hf signal |
WO2004004144A1 (en) * | 2002-06-28 | 2004-01-08 | Qualcomm Incorporated | Blind cancellation of cross-modulation by addition of modulated signal |
CN100380823C (en) * | 2002-06-28 | 2008-04-09 | 高通股份有限公司 | Blind cancellation of cross-modulation by addition of modulated signal |
Also Published As
Publication number | Publication date |
---|---|
EP1080535A1 (en) | 2001-03-07 |
AU3758099A (en) | 1999-11-16 |
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