Frequency agile filter concept for wireless whitespace receivers

Kählert, Stefan; Heinen, Stefan (Thesis advisor)

München / Hut (2014) [Dissertation / PhD Thesis]

Page(s): XVI, 145 S. : Ill., graph. Darst.


Current mobile communication systems allow data centric applications while the user is in transit. To guarantee high data throughput, the required bandwidth has to rise along with the user expectation. To avoid a bandwidth shortage, the 800MHz digital dividend has been released as LTE band over Europe. State-of-the-art modems employ a dedicated separate receiver per receive band, relying on external high quality filters to suppress out of band blockers. External filters limit the linearity requirements for the receiver and therefore also current and area consumptions. Both of them influence operation time, costs of the integrated circuit and competitiveness of the product. Goal must be to reduce the sheer amount of receive paths without increasing the power consumption of the receiver. In this thesis a frequency agile filter concept for mobile communication receivers has been investigated, that allows for full integration in a modern CMOS process. It is based on the frequency translation of a filter transfer function. The heart of the concept is a passive mixer and a capacitor, which can be regarded as a lowpass. The mixer translates the lowpass transfer function into the RF domain so that bandpass behaviour is achieved. Since each receiver is driven by an integrated frequency synthesizer, the centre frequency of the filter can easily shifted to the wanted receive band using a passive mixer. Large filter tuning ranges can be covered, limited by the tuning range of the synthesizer, only. Most importantly, the presented homodyne receiver has the advantage that the channel frequency and the synthesizer frequency are identical. The ultimate goal to avoid any external filters depends on the harmonic rejection of the receiver. Since mixers typically are driven by square wave signals, the harmonic rejection is low. High inherent harmonic rejection is therefore another important target for this work. Multiple testchips prove the functionality of the concept. Different LNA topologies as well as a complete receiver show a good performance in the measurements. The receiver covers a frequency range of 500 to 900 MHz with a flat gain and 8dB noise figure. The harmonic rejection is as high as 52 dB and concumes 47 mW Power.


  • URN: urn:nbn:de:hbz:82-opus-52418