Kaben’s Sampling IF (SIF) Filter replaces a traditional IF filter in a radio, or eliminates the need for several off-chip IF filters in multi-mode radios such as public security band radios.
In a receiver, a Sampling IF (SIF) filter 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. 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 as any adjacent channel Blocker has already been removed. This is illustrated in the diagram below.
Further, when a low IF receiver architecture is used, the SIF Filter provides a high RF image rejection without the use of digital correction techniques.
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 insensitivity to component mismatch is illustrated in the following Figure, where the Blue trace shows the effect of mismatch with respect to the ideal shown in Red.
The SIFs are suitable for integration into FM, WiMax, Wi-Fi, W-USB, GPS, Bluetooth, and RFID tag readers.