In this paper a differential single-port switched-RC N-path filter with bandpass characteristic is proposed. The switching frequency defines the center frequency, while the RC-time defines the bandwidth. This allows for high-Q highly tunable filters which can for instance be useful for cognitive radio. Using a linear periodically timevariant (LPTV) model, exact expressions for the filter transfer function are derived. The behavior of the circuit including non-idealities such as maximum rejection, spectral aliasing, noise and effects due to mismatch in the paths is modeled and verified via measurements. A simple RLC equivalent circuit is provided modeling bandwidth, quality factor and insertion loss of the filter. A 4-path architecture is realized in 65nm CMOS. An off-chip transformer acts as a balun, improves filter-Q and realizes impedance matching. The differential architecture reduces clock-leakage and suppresses selectivity around even harmonics of the clock. The filter has a constant -3dB bandwidth of 35MHz and can be tuned from 100MHz up to 1GHz. Over the whole band IIP3 is better than 14dBm, P 1dB =2dBm and NF<5.5dB,while the power dissipation increases from 2mW to 16mW (only clocking power).
-A passive switched capacitor RF bandpass filter with clock controlled center frequency is realized in 65nm CMOS. An off-chip transformer which acts as a balun, improves filter-Q and realizes impedance matching. The differential architecture reduces clock-leakage and suppresses selectivity around even harmonics of the clock. The filter has a constant -3dB bandwidth of 35MHz and can be tuned from 100MHz up to 1GHz. IIP3 is better than 19dBm, P 1dB =2dBm and NF<5.5dB at P diss =2mW to 16mW.Index Terms -N-path filters, commutated capacitor, CMOS bandpass filter, inductorless, cognitive radio, software-defined radio.
Abstract:Periodically time-variant passive 8-path notch filters are demonstrated in 65nm CMOS technology, with a notch frequency tunable from 100MHz to 1.2GHz with a clock signal. In a 50Ω environment, filter insertion loss in the pass band is 1.4-2.8dB, while the rejection at the notch frequency is >20dB.Given their P 1dB > +2dBm and IIP3> +17dBm, the filters can protect radio receivers from blocking over a wide tuning range. TextThe huge growth of the number of wireless devices makes wireless coexistence an increasingly relevant issue. If radios operate in close proximity, blockers as strong as 0dBm may occur, driving almost any receiver in compression (note that 0dBm in 50Ω corresponds to a pk-pk voltage of half a 1.2V supply). Thus RF blocker filtering is highly wanted. However, fixed filters are undesired when aiming for multi-band, software defined or cognitive radio transceivers. Passive LC filters show limited Q and tunability. Recently frequency translated filtering has been proposed as a potential solution direction for high Q filtering [1][2][3][4][5]. In [1,2] we showed that by applying the "N-path concept" 2[6], more than a decade of center frequency range with good linearity, compression point (P 1dB >0dBm, IIP3 >14dBm) and low noise is feasible for a bandpass (BP) filter. In [3] a notch filter with a combination of active and passive mixers is applied in a feedforward path realizing a BP filter.Moreover in [5] the low input impedance of a transimpedance amplifier with feedback is upconverted to create a notch filter at low frequencies (80MHz) suppressing TX leakage in an FDD system. In this work we explore the possibility to realize a notch filter applying the N-path concept at RF frequencies and in a completely passive way. A single-ended (SE) and a differential 8-path notch filter with passive frequency mixing are presented. The filters are power-matched in the input and output in the passband and provide a low insertion loss, high compression point and also low noise property, thus they can be utilized in front of a receiver to provide rejection of high power blockers with a large frequency tuning range. A prototype including a SE and a differential notch filter is implemented in 65nm CMOS technology (see Fig. 4.2.2 and 4.2.7). The circuit operates directly in a 50Ω system. In the differential architecture the notch is suppressed at the even harmonics of f s resulting in a wider passband. The second mixer in switches is set to 300mV to avoid reliability issues at high input swings). Larger switch would increase the insertion loss at high frequencies due to the parasitic capacitance and would require higher digital power drive. In the SE filter C 1 =7pF is chosen in each path targeting to suppress a 6MHz width blockers (e.g. TV channels in the cognitive radio or TV tuner applications). In the differential architecture two capacitors are in series and in order to get the same RC product as the SE version we have doubled the capacitor value (C 2 =14pF).For each filter, a divide-by-8 ring counter i...
Abstract:A 4-element LO-phase shifting phased-array system with 8-phase passive mixers terminated by baseband capacitors is realized in 65nm CMOS. The passive mixers upconvert both the spatial and frequency domain filtering to RF, realizing blocker suppression directly at the antenna input. 3rd harmonic reception is used to widen the frequency range to 0.6-3.6GHz at 68-195mW power dissipation. Up to +10dBm of P 1dB for out-of-beam/band, a 1-element NF of 3-6dB and in-beam/band IIP3=+2..+9dBm are measured. 2 TextMulti-antenna transceivers with beam-forming are recently gaining interest also for low GHz frequencies (<6GHz) [1]-[4]. In the antenna beam, (phase shifted) signals from multiple antennas add constructively, improving SNR, while out-of-beam signals add destructively (i.e. spatial filtering).Usually the summation point is behind some gain blocks, which then need to be capable of handling strong signals. To improve the input-referred compression point P 1dB , a fully passive switchedcapacitor approach was presented in [4], providing P 1dB =+2dBm, but at a high noise penalty:NF=18dB. Here we propose to sum immediately at the baseband capacitors of passive mixer-first switched-RC down-converters. We will show that this can render a direction dependent RF impedance (spatial filtering) together with RF band-pass frequency filtering at lower noise and higherThe proposed architecture is shown in Analog G m blocks consume 36mW generating 100mS at I and Q paths. Overall power when 4 elements are activated is 68-195mW for the received frequency range of 0.6-3.6GHz. The maximum ripple in the gain is 2.5dB and in-beam/band IIP3 varies from +2.. +9dBm (see Fig. 5.2.5). The first harmonic is rejected between 15-25dB. The measurement results are compared to three previously reported 4-element phased-array systems. Clearly remarkable P 1dB and NF are achieved, and the dynamic range at the antenna inputs is substantially improved compared to previous work.Acknowledgment:
-To reject strong interference in excess of 0 dBm, a 4-element LO-phase shifting phased-array receiver with 8-phase passive mixers terminated by baseband capacitors is presented. The passive mixers up-convert both the spatial and frequency domain filtering from baseband to RF, hence realizing blocker suppression directly at the antenna inputs. A comprehensive mathematical model provides a set of closed-form equations describing the spatial and frequency domain filtering including imperfections. A prototype is realized in 28 nm CMOS. It exploits 3 rd harmonic reception to achieve a wide RF-frequency range from 0.6-4.5 GHz at 34-119 mW power dissipation, while also providing impedance matching. Out of the band/beam, a 1 dB-compression point as high as +12/+10 dBm has been measured. The 1-element NF over the RF-frequency range is 4-6.3 dB, while in-beam/band IIP3 values of 0..+2.6 dBm are measured. This proposed technique can be instrumental to make RF receivers more robust for interference, while still being flexibly tunable in frequency.
Abstract-Radio transceivers capable of dynamic spectrum access require frequency agile transmitters with a clean output spectrum. High-Q filters are difficult to implement on chip and have limited tuning range. Transmitters with high linearity and broadband harmonic rejection can be more flexible and require less filtering. However, traditional Harmonic Rejection mixers suppress only a few harmonics. This paper presents an 8-path poly-phase transmitter, which exploits mixer-LO duty-cycle control and a tunable first-order RC low-pass filter to suppress ALL harmonics to below -40dBc. The optimum duty-cycle theoretically is 43.65% and a resolution of better than 0.1% is required to keep the spread in harmonic rejection within 1dB.We propose a simple monotonic duty-cycle control circuit and show by design equations and measurements that it achieves the required resolution over 3 octaves of frequency range. Also, analysis indicates that LO duty-cycle reduction compared to 50% improves power upconverter efficiency. A transmitter realized in 0.16m CMOS works from 100-800MHz at a maximum single tone output power of 10.8dBm with an efficiency of 8.7%, outperforming previous designs. The OIP3 is >21dBm, while the LO leakage and image rejection is better than -45dBc.
i SamenvattingAfstembare filters zijn zeer gewenst voor mobiele radio communicatie en de wens bestaat deze op chip te realiseren samen met de overige benodigde zend-en ontvangst hardware. Vooral nu mobiele apparaten vele verschillende draadloze communicatie mogelijkheden dienen te ondersteunen (denk bv. aan GSM, Bluetooth, WiFi, UMTS) geïntegreerd op één chip, is er dringend behoefte aan afstembare filters. Ook groeit het mobiele internet gebruik enorm, zodat behoefte bestaat aan programmeerbare radio hardware die op een slimmere manier met het schaars beschikbare radio spectrum omgaat. Dit heeft geleid tot het concept van een "cognitieve radio", een stuk radio hardware dat op een intelligente manier dynamisch het spectrum gebruikt. Zo'n cognitieve radio vraagt om flexibel programmeerbare afstembare filters en meer algemeen "software defined radio" (SDR) hardware.Het beperkte dynamische bereik van radio ontvangers vraagt om filtering van het radiosignaal direct bij de antenne. Dit filter dient de sterke ongewenste stoorsignalen te onderdrukken, die anders de radio ontvanger zodanig zouden oversturen dat door sterke vervorming betrouwbare draadloze communicatie onmogelijk wordt. Traditioneel wordt de filtering geïmplementeerd via aparte zgn. Surface Acoustic Wave (SAW) filters of Bulk Acoustic Wave (BAW) filters. Deze zijn echter relatief groot en duur vergeleken met een schakeling op een chip. Bovendien zijn ze voor een SDR grotendeels ongeschikt, daar ze een vaste (niet-afstembare) filter overdracht hebben. Op chip kunnen weliswaar LC filters gerealiseerd worden maar de kwaliteitsfactor Q van geïntegreerde spoelen is problematisch laag, terwijl "Qenhancement" en "gm-C" filter technieken een te beperkt dynamisch bereik hebben. Er bestaat dus een duidelijke onderzoek uitdaging om tot integreerbare flexibel programmeerbare filters te komen met een groot dynamisch bereik.In dit proefschrift worden zogenaamde "N-path" filters op basis van geschakelde RC circuits onderzocht. Deze filters gedragen zich als resonator voor frequenties rond hun schakelfrequentie, waarbij het mogelijk is zeer selectieve banddoorlaat of bandrejectie filters te maken. Het N-path filter concept past goed bij SDR omdat de filter frequentie digitaal te programmeren is via de schakelfrequentie, d.w.z. via een ii digitale programmeerbare klokfrequentie. Omdat nieuwe CMOS technologieën meer capaciteit per oppervlakte kunnen bieden, terwijl MOS schakelaars een lagere weerstand met minder parasitaire capaciteit kunnen hebben, profiteren N-path filters van Moore's law.Om de haalbaarheid van N-path filter voor SDR aan te tonen, is een 4-path differentieel switched RC banddoorlaat filter gerealiseerd, een 8-path single-ended filter en ook een differentieel bandstop (notch) filter, alle in 65nm CMOS technologie. Via mathematische analyse zijn de relevante filter overdrachten en ook diverse imperfecties geanalyseerd voor zowel N-path banddoorlaat en notch filters. Het geïmplementeerde banddoorlaat filter vertoont een gemeten IIP3 in-band >+14 dBm met ee...
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