Integrated Filters for Short Range Wireless and Biomedical Applications

Advances in VLSI technology combined with increase market demands to develop efficient portable devices have increased the interest in designing circuits that are capable to operate at low-voltage and/or low-power consumption. The design of analog and mixed-signal integrated circuits that can operate in a low-voltage environment with high performance is now imperative. This mainly stems from the continuous shrinking of device sizes, which leads to lower breakdown voltages and thus, in fact, circuits cannot operate with high voltages. Another reason is that modern applications require handheld devices with as small as possible dimensions and increased longevity, like the implantable pacemakers for the detection of cardiac signals and radio devices for short-range wireless communications. Also, co-integration of analog and digital circuits on the same chip, as required in modern mixed-signal system-on-chips (SoCs), implies that analog circuits must operate from supply voltages as low as digital ones. The International Technology Roadmap for Semiconductors (ITRS) [1] gives us a unique opportunity to look into the projected future of semiconductor technology and identify the design challenges. According to ITRS, by about the year 2013 and at the 32 nm technology node, the power supply for digital circuits will be at 0.5 V. Since the power consumption in digital circuits is proportional to the square of supply voltage, the continuous voltage scaling results in the reduction of overall power consumption. Of course, it should be noted that the reduction of supply voltage is mainly determined by the reliability of circuits, breakdown voltages and thermal problems; thus, they have to be appropriately scaled down.

This chapter presents a series of novel universal biquad topologies, where low-voltage current mirrors are employed as active elements. Due to current-mode nature of the performed signal processing, operations such as addition, subtraction, scaling and integration are very easily realized. Thus, the derived topologies consist of a small number of active elements contributing in lower power consumption, while they present the feature of low-voltage operation. The proposed universal biquads, which can be classified as either Single Input Multiple Output (SIMO) or Multiple Input Single Output (MISO), provide the five standard filter functions (lowpass, highpass, bandpass, bandstop and allpass) from the same configuration. Other advantages of the derived topologies are the absence of passive resistors, the resonant frequency of the filters can be electronically controlled by an appropriate dc current and only grounded capacitors are needed for the integrators. In addition, some of the proposed filters offer the feature of orthogonal adjustment between the resonant frequency and the quality factor. The behavior evaluation of the proposed universal biquads has been performed through a test chip prototype fabricated in AMS 0.35 μm CMOS technology.

The design of low-voltage complex filters using current mirrors for wireless receivers is presented in this chapter. Complex signal processing is an attractive technique for removing the image signals that appear in transceiver architectures. The problem from the presence of image signal in low-IF architectures is caused by the down-conversion operation realized by complex mixing. The realization of complex filters is achieved by employing an appropriate transformation to the corresponding conventional real filters. Two systematic methods for designing high-order complex filters are presented i.e. the leapfrog and the topological emulation techniques, where the employed active elements are low-voltage current mirrors. Thus, like in previous chapter, the offered benefits are the capability of low-voltage operation, the electronic tuning of their frequency responses and the absence of resistors. A twelfth-order complex filter function has been realized by employing the aforementioned techniques, where the performance of the corresponding topologies, fabricated in AMS 0.35 μm CMOS process, has been experimentally verified. Also, a detailed test setup for the measurement of the fabricated chip, including the interface for V/I and I/V conversion, is also provided.

This chapter focuses on the design of novel topologies that are suitable for realizing wavelet filter functions. These filters are extensively used in several biomedical applications and especially in low-voltage/low-power implantable devices for the detection and analysis of cardiac signals. As in previous chapters, low-voltage current mirrors will be employed as active elements, providing, thus, the advantages of resistorless topologies and the electronic adjustment capability of their frequency characteristics. In addition, by using MOS transistors biased in subthreshold region, there is the benefit of ultra low-voltage (0.5 V) operation. The efficiency of the proposed filters is verified through simulation results by employing TSMC 130 nm CMOS process, where the most important performance factors are considered.

This chapter focuses on the design of an adjustable low-voltage current mirror. The presented topology provides continuous gain adjustment, while it simultaneously features the attractive characteristic of low-voltage operation. The behavior of the current mirror has been experimentally verified through a first-order lowpass filter fabricated in AMS 0.35 μm CMOS technology.

This book describes the design of low-voltage analog integrated filters using current mirrors, one of the most common building blocks in analog and mixed-signal VLSI circuits. Its purpose is to contribute in the existing research area of the design of analog filters using low-voltage current mirrors. In this direction, all the derived filters are constructed by the low-voltage high-swing current mirror, offering the advantages of low-voltage operation, absence of passive resistors and electronic adjustment capability of their frequency characteristics. Several design examples have been described in detail, namely universal biquad filter topologies, complex filters for Bluetooth/ZigBee low-IF receivers, wavelet filters for cardiac signal detection and a current mirror topology with electronically adjustable gain. Experimental results from the fabricated chips have been also presented, exhibiting their utility in modern low-voltage low-power portable devices.