TABLE OF CONTENTS Monolithic filters in the frequency range of 100 kHz to 10 MHz have many applications in communication receivers and video processing as well as in data communications and local area networks [147], [150], [151], [152], [153], [154], [155], [157], [158], [159], [166]. In general, design techniques that are applicable to voice band applications do not perform properly in this frequency range. They become even more difficult to extrapolate as the voltage supply limits are pushed down, because the maximum values of the currents that devices can provide is more restricted. The consequence of this is the degradation of the high frequency range.
This section covers the design of an FGMOS filter operating in the range of megahertz at 1.25 V power supply voltage. As it was explained in previous designs along this book, the FGMOS can be used as an alternative to MOS with a reduced effective threshold voltage. Hence, higher current levels will be possible which increases the upper reachable frequency limit. Besides, the transistor facilitates the common mode feedback mechanism without introducing extra distortion.
Let us consider the circuit in Fig. 5.18 with two equal FGMOS transistors (M1 a, M1 b) operating in the strong inversion saturation region [215]. The drain to source currents of transistors M1 a and M1 b can be expressed as [50]
