Reconfigurable Radio Architecture Kaben's unique radio architecture enables transceiver front ends to be reconfigurable, and thereby to support multiple standards. This innovative technology occurs in the Intermediate Frequency (IF) range between the RF and the digital. The Reconfigurable IF is built around three novel circuit cores; a Sampling IF Filter (SIF) which converts an IF of choice directly to digital, a Digital-to-IF (DIF) up-converter which converts a digital baseband directly to an IF of choice, and an ultra-low phase noise and spur level synthesizer. The field programmable flexibility of the Reconfigurable IF not only provides a multi-standard transceiver capability, it also relaxes the associated component specifications, such as the carrier frequency up- and down-converters, the low noise amplifier, and the external power amplifier, for both single standard and multi-standard application. The Reconfigurable IF also removes the need for external SAW filters, while providing all the strengths of a classic super heterodyne architecture. The combination of field programmable flexibility and lower component count, results in a quick time-to-market and a reduced BOM. When using a super heterodyne approach, the Reconfigurable IF eliminates the analog baseband of traditional transceiver design, by converting directly between IF and digital. For the receiver, this avoids DC offset and IP2 problems, and removes the need for compensation loops in the digital back-end. The elimination of the analog baseband also removes issues associated with 1/f noise. Avoiding the integrated excess noise (of approximately 12 dB) allows a reduced gain requirement for the LNA, and reduced RF power levels at all points in the receiver. Reduced RF power levels provide higher linearity, which ultimately yields higher performance (lower bit error rate).  The Kaben transceiver front end based on the three key technologies of the SIF, the DIF, and the synthesizer is truly versatile. It is capable of performing with radio standards ranging from Bluetooth (narrow band and low dynamic range) through WiMax and Wireless USB (wide band and high dynamic range).
Sampling IF Filters (SIF) The Sampling IF (SIF) filter in the receiver actually performs several operations simultaneously. Its principal function is to provide channel select filtering. In addition, the SIF provides image reject filtering, anti-aliasing filtering, AGC, sampling, and digitization. As a result of the SIF Filter removing adjacent or near channel blockers prior to digitization is that the dynamic range and bandwidth (sampling rate) of the digital output is significantly reduced. 
For the transmitter, elimination of the analog baseband removes the need for dual (I & Q) up-converters. A single, complex modulated, IF signal is produced from the two (I & Q) digital baseband signals. As a result of this digital-to-RF (DIF) conversion, the need for two up-converter chains, as well as the need for amplitude and phase calibration and correction loops is removed. The removal of an analog baseband signal also eliminates any prospect of VCO pulling due to stray DC signals on the chip. For the transmitter, elimination of the analog baseband removes the need for dual (I & Q) up-converters. A single, complex modulated, IF signal is produced from the two (I & Q) digital baseband signals. As a result of this digital-to-RF (DIF) conversion, the need for two up-converter chains, as well as the need for amplitude and phase calibration and correction loops is removed. The removal of an analog baseband signal also eliminates any prospect of VCO pulling due to stray DC signals on the chip. Finally, a digital-to-RF (DIF) converter in the transmitter path of a radio transceiver can be readily combined with an RF-to-digital (SIF) converter in a sense path attached to the output of the power amplifier, to provide adaptive pre-distortion linearization. Kaben's field programmable SIF can tune to a center frequency anywhere between DC and 1200 MHz. The bandwidth is selectable from 200 kHz to 40 MHz, while adjacent channel stop band attenuation can be chosen from -55 dB to -70 dB. The gain setting of the SIF can be varied from 4 dB to 100 dB. The SIF is resistant to temperature and process variations. A 10% mismatch in capacitor and resistor values has no effect on the passband response and corner frequency, and only a 10 dB increase in adjacent channel stop band attenuation.  This novel technology combines anti-alias filtering with sub-sampling to provide a low power anti-alias filter, channel selection filter, image reject filter, AGC, sampler, and A/D in one unit. The SIFs have an input frequency up to 1200 MHz with up to 40 MHz bandwidth suitable for integration into FM, WiMax, Wi-Fi, W-USB, GPS, Bluetooth, and RFID tag readers. The SIF Filter replaces a traditional IF filter in a radio or eliminates several off-chip IF filters in multi-mode radios. In public security band radios, the programmability of a SIF Filter eliminates the need for multiple off-chip crystal filters.  When low IF receiver architectures are used, the SIF Filter provides a high RF image rejection without the use of digital correction techniques. The Sampling IF filter is based on Kaben's patented Sampled RF Finite Impulse Response (FIR) technology. This technology is the RF equivalent of a digital baseband FIR filter. As such, center frequency, bandwidth, pass band ripple and adjacent channel attenuation can all be preselected to meet performance specification. Unlike traditional, un-tunable RF filters, the Sampled RF Finite Impulse Response technology provides a pass band response with no frequency dispersion similar to a digital baseband FIR filter. The major blocks of the simplified Sampled RF Finite Impulse Response filter are shown in the accompanying figure. First, the RF input signal is applied to a bank of parallel RF transconductance amplifiers, each of which produces an RF current source that is weighted by a predetermined complex coefficient. The weighted RF current sources are then applied to an RF switching network, which sequentially "rotates" each weighted RF current source output to one (or more) parallel integrators. The outputs of the individual integrators are then sequentially clocked to a sampler, which provides the filtered, sampled analog, baseband representation of the input pass band RF signal.  A simplified example of the new, on-chip, reconfigurable RF filter is shown in the figure. This filter is comprised of four major elements: a current replicator, that generates multiple tap currents, each proportional to an input signal through constants TC0, TC1, and TC2; a "current rotator", that sends the tap currents to multiple integrators; multiple integrators, where the number of integrators is one more than the number of tap currents; and an output sampling and resetting circuit. The tap current coefficients chosen determine the filter response,  that is achieved:  Here:  and  are the tap coefficients. The current rotator that is connected to the tap currents, consists of a switch matrix, which is an array of switches coupled between any of the tap currents and any of the following integrators. Each of the integrators, CI[0], CI[1], CI[2], and CI[3] consists of an operational amplifier and a capacitor. Finally, the output sampling and resetting circuit, which selects the correct integrator output at the correct sampling time, consists of output select switches, Ss1, Ss2, Ss3, etc. Each of the integrators in the sampling RF filter periodically goes through two operating phases; an integrating phase, during which there is at least one current being received, and a rest phase, when no tap current is received. During the rest phase, the integrator's charge is sampled by observing the voltage at its output. This is done by closing the corresponding output sampling switch, connecting the integrator to the subsequent circuits. The voltage on the integrating circuit output is then reset using its reset switch. Figure 2 shows the timing diagram for the state changes of the 4 clock buses used in the current rotator of the filter shown in Figure 1. Here, for example, when CK[0] is high, the current from TC0 is integrated onto CI[0], then during the time when CK[1] is high, TC1 is integrated onto CI[0], etc. The performance of a 140 MHz center frequency, bandpass filter having 256 tap currents, is shown in Figure 3 (over a wide frequency range), and in Figure 4 (around the pass band). As expected for a sampling filter, undesired pass bands exist on both sides of the sampling frequency. Since the sampling frequency being use by the filter is high (1.61 GHz), these unwanted pass bands are far from the desired pass band. Furthermore, these unwanted pass bands are attenuated by the inherent sinc function operation of the integrating sampler. As can be seen in Figure 4, a 3 dB bandwidth of 10 MHz is achieved, with excellent pass band ripple (less than +/- 0.5 dB), and excellent adjacent band attenuation (greater than 64 dB). Digital to IF Converters (DIF) Kaben's field programmable DIF can provide an IF output up to 300 MHz, and a bandwidth up to 20 MHz. The DIF provides a spurious free dynamic range of 60 dB, and an image rejection of 60 dB. The DIF includes integrated, semi-digital FIR filters which eliminates aliased signals, removes quantization noise, and provides pass band sin x/x correction. High linearity (12 bits) and zero phase dispersion are provided by the DIF. 
The Converter accepts a digital baseband input and upconverts the signal to an IF frequency, up to 400 MHz. The in-phase and quadrature digital input can have up to 2 MHz bandwidth each, for a combined 4 MHz bandwidth. Five of the 4 MHz cells can be stacked (in parallel) to provide 20 MHz total bandwidth. When stacked, the digital baseband inputs are fed directly into the cells, each of which is tuned to an individual 4 MHz band. Each cell in turn provides 50 dB of rejection of all adjacent bands. The high IF frequency reduces the requirement for off-chip RF output filtering, thereby reducing cost and size. The high linearity of 12 bits and spurious free dynamic range of 60 dB makes this product an ideal selection for transmitters employing complex modulation formats such as OFDM and high data-rate multi-level QAM. 
The Digital-to-IF Converter inherently provides band-pass and anti-aliasing filtering with zero phase dispersion, thereby delivering undistorted up-conversion of the digital baseband complex signal. For advanced signal structures supporting high data rates such as OFDM, generating the up-converted transmit signal with zero dispersion is crucial in maintaining acceptable bit error rate performance. Using high IF frequencies simplifies the off-chip RF filters because the image frequency and the LO frequency will be farther away from the desired output frequency. The Image Rejection of 60 dB and Spurious Free Dynamic Range (SFDR) of 60 dB is useful in OFDM and QAM transmitter architectures. This unique ∆∑ DAC eliminates the issue of quantization noise by removing it with an integrated on-chip FIR Filter. The DAC and FIR Filter provides adjacent band rejection of 50 dB. Layout of the design can be performed in a customer's standard digital flow by incorporating Kaben's customized cells into the libraries that are used by the auto place and route software. The DIF is ideal for WiMAX 802.16a, WLAN (Wi-Fi) 802.11a, 802.11b, 802.11g, 802.11h, and 802.11n, Bluetooth, Software Defined Radios (SDR), Multi-mode Radios, and Cable Modem products. The major blocks of the Digital-to-IF converter are shown in the accompanying figure. First, multi-bit (typically 10 bits) digital I (in-phase) and Q (quadrature-phase) data streams are up-sampled, and reduced in their number-of-bits (to typically 2 bits) in the dual ∆∑ converters. The ∆∑ converters provide the up-sampling while relegating the quantization noise to out-of-band frequencies. They also convert each (typically 2 bit) output signal into parallel circuit tracks (typically 3) representing the possible 4 values of the output. A circuit track representing the zero value is not required in the subsequent Semi-digital filters, and hence is not included. Dynamic Element Matching is used in this process to eliminate the non-linear effects of component mismatch. The two outputs from the two ∆∑ converters are then passed to two semi-digital FIR filters. Architecturally, each semi-digital FIR filter is identical to a classic FIR digital filter, except that the weighting coefficients at the output of each delay stage are parallel one-bit analog-to-digital converters (typically 3) attached to the parallel circuit tracks. The analog outputs from the parallel one-bit analog-to-digital converters at all delay tap outputs of the FIR structure are then summed together to form a filtered analog version of the digital baseband input signal. Further, due to the up-sampling, the FIR filter response can be chosen to select the desired analog IF bandpass (aliased) replica of the digital baseband input, thereby achieving up-conversion from baseband The two (I and Q) IF bandpass signals are then combined and provided to the analog IF input to the transmitter's up-conversion mixer. Providing the high frequency clock for the ∆∑ converters and the semi-digital filters can be readily achieved using a delay-locked loop driven with a low frequency reference clock. As in all sampling techniques, the delay-locked loop installs a sin x / x weighting onto the baseband signals tailored to selecting the desired alias. This can easily be refined for by adjustment to the tap coefficient weights at each delay element output in the semi-digital FIR filter to obtain a filter sufficiently narrow to suppress quantization of the ∆∑ converter. PLL Synthesizers & VCOs With synthesizer designs encompassing Integer-N, Fractional-N, and Delta-Sigma Fractional-N. Kaben can deliver the right drop-in for any SoC requirement. The cells are tailored for applications that require low power consumption, excellent phase noise, fine step size, low spurious, and fast switching speeds. The ∆∑ synthesizer cells operate using crystal frequencies up to 50 MHz and generate outputs from 400 to 6000 MHz with step sizes less than 25 Hz. The low phase noise of -93 dBc/Hz at 2 kHz offset for a 6 GHz output (when using a 20 MHz reference) and the low spurious response of -80 dBc means these cells can be used in WiMAX 802.16a systems. The company also produces narrow band VCO designs that are complementary to the synthesizers. These VCOs and the Delta-Sigma Fractional-N synthesizers are integrated to offer Local Oscillators targeted for: WiMAX 802.16, WLAN (Wi-Fi) 802.11a, 802.11b, 802.11g, 802.11h, and 802.11n, Bluetooth, Software Defined Radios (SDR), Multi-mode Radios, and Cable Modem products.  |
