Source: http://www.google.com/patents/US6404293?dq=5,815,794
Timestamp: 2014-10-25 07:04:18
Document Index: 318515543

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60']

Patent US6404293 - Adaptive radio transceiver with a local oscillator - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn oscillator circuit is disclosed which includes an oscillator to generate a first signal having a first frequency, a second oscillation source to generate a second signal having a second frequency, the second oscillator comprising a frequency divider coupled to the oscillator, and a mixer to mix to...http://www.google.com/patents/US6404293?utm_source=gb-gplus-sharePatent US6404293 - Adaptive radio transceiver with a local oscillatorAdvanced Patent SearchPublication numberUS6404293 B1Publication typeGrantApplication numberUS 09/691,633Publication dateJun 11, 2002Filing dateOct 18, 2000Priority dateOct 21, 1999Fee statusPaidAlso published asUS6417737, US6608527, US7031668, US7555263, US7720444, US7970358, US8041294, US20030042984, US20030067359, US20060205374, US20090286487, US20100295598Publication number09691633, 691633, US 6404293 B1, US 6404293B1, US-B1-6404293, US6404293 B1, US6404293B1InventorsHooman Darabi, Ahmadreza Rofougaran, Maryam RofougaranOriginal AssigneeBroadcom CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (6), Non-Patent Citations (1), Referenced by (61), Classifications (25), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetAdaptive radio transceiver with a local oscillatorUS 6404293 B1Abstract An oscillator circuit is disclosed which includes an oscillator to generate a first signal having a first frequency, a second oscillation source to generate a second signal having a second frequency, the second oscillator comprising a frequency divider coupled to the oscillator, and a mixer to mix to the first and second signals, wherein the oscillator, frequency divider and mixer are each quadrature. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or the meaning of the claims.
CROSS-REFERENCE TO RELATED APPLICATION The present application is a continuation of co-pending patent application Ser. No. 09/634,552, filed Aug. 8, 2000, priority of which is hereby claimed under 35 U.S.C. �120. The present application also claims priority under 35 U.S.C. �119(e) to provisional Application Nos. 60/160,806, filed Oct. 21, 1999; Application No. 60/163,487, filed Nov. 4, 1999; Application No. 60/163,398, filed Nov. 4, 1999; Application No. 60/164,442, filed Nov. 9, 1999; Application No. 60/164,194, filed Nov. 9, 1999; Application No. 60/164,314, filed Nov. 9, 1999; Application No. 60/165,234, filed Nov. 11, 1999; Application No. 60/165,239, filed Nov. 11, 1999; Application No. 60/165,356; filed Nov. 12, 1999; Application No. 60/165,355, filed Nov. 12, 1999; Application No. 60/172,348, filed Dec. 16, 1999; Application No. 60/201,335, filed May 2, 2000; Application No. 60/201,157, filed May 2, 2000; Application No. 60/201,179, filed May 2, 2000; Application No. 60/202,997, filed May 10, 2000; Application No. 60/201,330, filed May 2, 2000. All these applications are expressly incorporated herein by referenced as though fully set forth in full.
In the described exemplary embodiment, the RF clocks are generated in the in the LO generator 14. This can be accomplished in various fashions including, by way of example, either generating the RF clocks in the VCO or using a polyphase circuit to generate the RF clocks. Regardless of the manner in which the RF clocks are generated, the mixer 52 will produce a spectrum of frequencies including the sum and difference frequencies, specifically, fVCO�(1+(1/N)) and its image fVCO�(1−(1/N)). To reject the image, the mixer 52 can be configured as a double quadrature mixer as depicted in FIG. 3. The double quadrature mixer includes one pair of mixers 55, 57 to generate the Q-clock and a second pair of mixers 59, 61 to generate the I-clock. The Q-clock mixers utilizes a first mixer 55 to mix the I output of the VCO 48 (see FIG. 2) with the Q output of the divider 40 and a second mixer 57 to mix the Q output of the VCO with the I output of the divider. The outputs of the first and second mixers are connected together to generate the Q-clock. Similarly, the I-clock mixers utilizes a first mixer 59 to mix the I output of the divider with the Q output of the VCO and a second mixer 61 to mix the Q output of the divider with the I output of the VCO. The outputs of the first and second mixers are connected together to generate the I-clock. This technique provides, very accurate I-Q clocks by combination of quadrature VCO and filtering. Because of the quadrature mixing, the accuracy of the I-Q clocks is not affected by the VCO inaccuracy, provided that the divide by N circuit generates quadrature outputs. This happens for even divide ratios, such as N=2.
Exemplary Embodiments of a Local Oscillator In embodiments of the present invention utilizing a low-IF or direct conversion architecture, techniques are implemented to deal with the potential disturbance of the local oscillator by the PA. Since the LO generator has a frequency which coincides with the RF signal at the transmitter output, the large modulated signal at the PA output may pull the VCO frequency. The potential for this disturbance can be reduced by setting the VCO frequency far from the PA output frequency. To this end, an exemplary embodiment of the LO generator produces RF clocks whose frequency is close to the PA output frequency, as required in a low-IF or direct-conversion architectures, with a VCO operating at a frequency far from that of the RF clocks. One way of doing so is to use two VCO 864, 866, with frequencies of f1 and f2 respectively, and mix 868 their output to generate a clock at a higher frequency of f1+f2 as shown in FIG. 4. With this approach, the VCO frequency will be away from the PA output frequency with an offset equal to f1 (or f2). A bandpass filter 876 after the mixer can be used to reject the undesired signal at f1−f2. The maximum offset can be achieved when f1 is close to f2.
Cos(ω1 t)�⅓ Sin(3ω1 t)−Sin(ω1 t) ⅓ Cos(3ω1 t)→−⅓ Sin(2ω1 t) (48)
For N=2, the LO generator output will have a frequency of 1.5f1, and the closest spurs will be located �f1 away from the output. These spurs can be rejected by positioning LC filters (not shown) at the output of each circuit in the LO generator. A second-order LC filter tuned to f0, with a quality factor Q, rejects a signal at a frequency of f as given in the following equation:  H  ( f )  = f Qf 0 [ 1 - ( f f 0 ) 2 ] 2 + ( f Qf 0 ) 2 ( 49 ) The following discussion changes based on the Q value. Considering a Q of about 5 for the inductor, with f0=1.5f1, the spur located at 2.5f1 is rejected by about 15 dB by each LC circuit. This spur is produced at the LO generator output due to the mixing of the VCO third harmonic (at 3f1) with the divider output (at 0.5f1). This signal is attenuated by 10 dB since the third harmonic of a square-wave is one third of the main harmonic, 15 dB at the LC resonator at the mixers output tuned to 1.5f1, and another 15 dB at the output of the buffers (900, 902 in FIG. 7). This gives a total rejection of 40 dB. When applied to the mixers in the transmitter, this LO generator output will upconvert the baseband data to 2.5f1. With LC filters (not shown) positioned at the upconversion mixers and PA output in the transmitter, another 15+15=30 dB rejection is obtained (FIG. 7).
FIG. 8 shows a signal passing through a limiting buffer 910 (such as the buffers implemented in the LO generator). When a large signal at a frequency of f accompanied with a small interferer at a frequency of Δf 902 away pass through a limiting buffer, at the limiter output the interferer produces two tones �Δf 914, 916 away from the main signal, each with 6 dB lower amplitude. Therefore, the spur at 2.5f1 will actually be 10+15+15+6=46 dB attenuated when it passes through the buffer, instead of the 40 dB calculated above. It will also produce an image at 0.5f1 which is 10+15+22+6=53 dB lower than the main signal. This will dominate the spur at 0.5f1 because of the third harmonic of the divider mixed with the VCO signal, which is more than 75 dB lower than the main signal.
Vout � 1=Cos(ω2 t)�Cos(ω1 t+θ)−Sin(ω2 t)�Sin(ω1 t) (50)
Vout � Q=Cos(ω2 t)�Sin(ω1 t)+Sin(ω2 t)�Cos(ω1 t+θ) (51) where ω1 is the VCO radian frequency, and ω2 is the divider radian frequency, equal to 0.5ω1. By simplifying equation (25) and equation (26), the signals at the output of mixers will be: V out �  I = - Sin  ( θ 2 ) � Sin  ( ( ω 1 - ω 2 )  t + θ 2 ) + Cos  ( θ 2 ) � Cos  ( ( ω 1 + ω 2 )  t + θ 2 )   and ( 52 ) V out �  Q = - Sin  ( θ 2 ) � Cos  ( ( ω 1 - ω 2 )  t + θ 2 ) + Cos  ( θ 2 ) � Sin  ( ( ω 1 + ω 2 )  t + θ 2 ) ( 53 ) The above equations show that regardless of the value of θ, the outputs are always in quadrature. However, other effects should be evaluated. First, a spur at ω1−ω2=0.5ω1 is produced at the output. This spur can be attenuated by 2�22=44 dB by the LC filters at the mixer and its buffer outputs. Thus, for 60 dB rejection, the single sideband mixers need to provide an additional 16 dB of rejection (about 0.158). Based on equation (53), tan(θ/2)=0.158, or θ≈18�, phase accuracy of better than 18� can generally be achieved. Second, phase error at the VCO output lowers the mixer gain (term Cos(θ/2) in equation (52) or (53)). For a phase error of 18�, the gain reduction is, however, only 0.1 dB, which is negligible. For θ=90� (a single-phase VCO), both sidebands are equally upconverted at the mixer output. However, the LC filters reject the lower sideband by about 44 dB. The mixer gain will also be 3 dB lower. This will slightly increase the power consumption of the LO generator. If θ=180� (the VCO I and Q outputs are switched), the lower sideband is selected, and the desired sideband is completely rejected.
Similarly, the LO generator will not be sensitive to the phase imbalance of the divider outputs if the VCO is ideal. However, if there is some phase inaccuracy at both the divider and VCO outputs, the LO generator outputs will no longer be in quadrature. In fact, if the VCO output has a phase error of q1 and the divider output has a phase error of q2, the LO generator outputs will be: V out �  I = - Sin  ( θ 1 - θ 2 2 ) � Sin  ( ( ω 1 - ω 2 )  t + θ 1 - θ 2 2 ) + Cos  ( θ 1 + θ 2 2 ) � Cos  ( ( ω 1 + ω 2 )  t + θ 1 + θ 2 2 )   and ( 54 ) V out �  Q = - Sin  ( θ 1 + θ 2 2 ) � Cos  ( ( ω 1 - ω 2 )  t + θ 1 - θ 2 2 ) + Cos  ( θ 1 - θ 2 2 ) � Sin  ( ( ω 1 + ω 2 )  t + θ 1 + θ 2 2 ) ( 55 ) This shows that the outputs still have phases of 0 and 90�, but their amplitudes are not equal. The amplitude imbalance is equal to: Δ   A A = 2  Cos  ( θ 1 + θ 2 2 ) - Cos  ( θ 1 - θ 2 2 ) Cos  ( θ 1 + θ 2 2 ) + Cos  ( θ 1 - θ 2 2 ) = 2  tan  ( θ 1 2 ) � tan  ( θ 2 2 ) ( 56 ) If θ1 and θ2 are small and have an equal standard deviation, that is, the phase errors in the VCO and divider are the same in nature, then the output amplitude standard deviation will be: σ A ≈ ( σ θ ) 2 2 ( 57 ) where σA is the standard deviation of the output amplitude, and σ0 is the phase standard deviation in radians. Equation (57) denotes that the phase inaccuracy in the VCO and divider has a second order effect on the LO generator. For instance, if θ1 and θ2 are on the same order and about 10�, the amplitude imbalance of the output signals will be only about 1.5%. In this case, the lower sideband will be about 15 dB rejected by the mixers, which will lead to a total attenuation of about 22+22+15=59 dB. This shows that the LO generator is robust to phase errors at the VCO or divider outputs, since typically phase errors of less than 5� can be obtained on chip.
Any amplitude imbalance in the signals at the VCO and divider output will only cause a second order mismatch in the amplitude of the LO generator signals, and the output phase will remain 0 and 90�. If the standard deviation of the amplitude imbalance at the VCO and divider are the same and equal to σa, then the standard deviation of the LO generator output amplitude imbalance (σA) will be: σ A = ( σ α ) 2 2 ( 58 ) The reason phase inaccuracy is more emphasized here is that because of the limiting stages in the LO generator and the hard switching at the mixers LO input, most of the errors will be in phase, rather than amplitude.
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