TABLE OF CONTENTS This section outlines the role of filters in typical wireless transceiver architectures, and some of the important parameters in their design. The need for on-chip tuning in virtually all practical applications of integrated filters is then discussed.
A typical single-chip wireless transceiver design requires several different filters; possible architectures for a receiver and transmitter are shown in Figures 6.1 and 6.2 respectively [3]. In Figure 6.1, the signal input from the antenna is bandpass filtered at the signal frequency, typically in the VHF/UHF range. This defines the bandwidth of the receiver frontend, and reduces unwanted responses, such as the image response in the case of the superheterodyne architecture. Many designs rely on impedance matching networks associated with the low-noise amplifier to provide sufficient selectivity, but in more demanding applications additional filters are require. The majfor challenge or integrated RF filter design is the high operating frequency; for example, GSM handsets operating around 900 MHz, Bluetooth at 2.45 GHz. Operation at these frequencies pushes the capabilities of current IC technologies, and circuit parasitics have a serious adverse effect on the response of the filter, making predictable performance difficult to achieve.
The signal is then down-converted to an intermediate frequency (IF), where further bandpass filtering occurs. Traditionally, the IF bandpass filter performs the channel filtering function before the signal is demodulated; in modern receiver designs this function is...
