This paper proposes to study the design of a novel high-Q fully integrated switched capacitor bandpass filter. This circuit, implemented in CMOS technology, allows a tunable high selectivity over a broad frequency band. The proposed architecture is intended to replace passive surface acoustic wave (SAW) filters in low-cost wireless radio-communication applications. To show the feasibility of the proposed filter a prototype has been fabricated and tested. Measurements show quality factors up to 300, and a tunable center frequency range of 290 MHz [240 - 530 MHz] with a bandwidth tuning.

Fully Integrated High-Q Switched Capacitor Bandpass Filter with Center Frequency and Bandwidth Tuning

A novel approach in the design of high-frequency switched capacitor (SC) circuits is presented. It is based on the use of simple and fast amplifiers with low but precisely controlled gain value. The effect of the precisely known and stable opamp gain is compensated for by changing the capacitor values during the synthesis of the SC cell. An example of an opamp with these features and the synthesis of a biquadratic filter based on this approach are given.

BiCMOS operational amplifier with precise and stable DC gain for high-frequency switched capacitor circuits

This paper describes a fifth-order, low-pass switched capacitor filter for video applications. It has a 4-MHz cutoff frequency and uses a parallel biquadratic structure with double sampling to achieve an 80-MHz input sampling rate in a 2-/spl mu/m CMOS process. The prototype filter is fully differential, occupies an active area of 11 mm/sup 2/, and dissipates 190 mW. >

An 80-Msample/s video switched-capacitor filter using a parallel biquadratic structure

Currently unwanted excitation of higher-order transverse modes is the most serious drawback of vertical-cavity surface-emitting diode lasers (VCSELs) limiting their possible applications. In the present paper, various methods used to suppress those modes are described and their effectiveness is compared. It is well known that, because of a nearly uniform current injection into their active regions, small-aperture VCSELs without any modification offer quite high single-fundamental-mode (SFM) output. However, their series resistance is often too high, which aggravates their high-modulation performance. Similarly uniform current injection may be also achieved with the aid of a tunnelling junction. Generally, methods suppressing higher-order modes take advantage of higher optical gain within the central part of the active region, higher radiation losses outside this region and/or higher central mirror reflectivity. Currently, applications of a tunnel junction, an impurity-induced disordering or an inverted shallow surface relief seem to be the simplest and the most effective methods. The deep etched holey structure or the ARROW structure enable obtaining similar single-mode output powers but they may be used in special cases only because of their complex technology. Photonic crystals may probably enable more advanced mechanisms of suppressing higher-order modes in future because currently their application seems to be still far from being optimised.

VCSEL structures used to suppress higher-order transverse modes

A new negative current mirror using n-channel GaAs MESFETs is proposed. The circuit combines the advantages of linearity and good high frequency performance. Applications are as a general high speed circuit building block and for high frequency amplification.

High frequency gallium arsenide current mirror

The letter presents experimental results for a second order switched capacitor bandpass filter designed to operate with a 250 MHz switching frequency and implemented using gallium arsenide (GaAs) technology. Measurements on a chip fabricated in a 0.5 μm GaAs process confirm that the filter design, amplifier and switching components meet the desired performance specifications. The filter operates with high precision at 300 MHz and bandpass filtering at a switching frequency of 400 MHz is demonstrated.

K. Steptoe

Papers

400 MHz switching rate GaAs switched capacitor filter