Hacer Atar Yildiz

On the Realization of MOS-Only Allpass Filters

The objective of this paper is to present a simple filter topology, which can be used to implement first- and second-order MOS-only allpass filters. The resulting filters realize the allpass functions without using any external passive components; hence these occupy very small chip area and are capable of operating at high frequencies. Cadence Spectre simulation and experimental results verifying the main advantages of the filters are provided.

Design considerations of MOS-only allpass filters

In this paper, a simple filter topology that can be used to implement first-order MOS-only allpass filter is proposed. The proposed MOS-only allpass filter offers inherently very accurate magnitude and phase characteristics at very high frequencies. However, MOS-only active filter suffers from an inherent low frequency limitation. In order to address this issue, the modification technique allowing the derivation of MOS-only filter which allow extension of the operating frequency towards lower frequency region is proposed. Detailed simulations results of the filter modified according to the proposed technique are also provided in order to verify the usefulness of the theoretical approach.

MOS-only allpass filters modified for low operating frequency range

The objective of this paper is to present a modification technique that can be used to alleviate the low-frequency limitations of MOS-only filters. The technique is based on adding an additional pair of cross-coupled transistors to modify the time constant of the filter. In this case, lower frequency operations is attainable without having to use large transistors with higher intrinsic capacitors; hence the chip area occupied by the circuit is kept low. Two existing MOS-only filter circuits are modified to illustrate the versatility of the idea and Spectre simulation results are provided in order to show the proper operation of the circuits.

MOS-only polyphase filter with small chip area

In this paper, it is aimed to realize a systematic approach for the realization of the MOS only complex polyphase filters which occupy small chip area. For this purpose, we used a technique based on adding cross-coupled transistors realizing local positive feedback, which, in turn, increases filter time constants. Thanks to this method, a substantial reduction in the filter chip area is achieved without having to use bulky on chip capacitors. The usefullness of the approach is validated by comparing the layouts of the designed CMOS circuit with the conventional RC polyphase filter. Post-layout simulation results using SPECTRE in CADENCE design environment are provided to verify feasibility of the proposed complex filter.

On the design of MOS-only complex filter

In this paper, a new area-effective complex-filter topology which can be used as an image-reject filter in low-IF receiver is proposed. A first-order image-reject filter obtained according to a new topology which corresponds to a complex shunt RC circuit. To demonstrate the usefulness of filter, simulation results of the filter are obtained by using SPECTRE in the CADENCE design tool.

A new active only integrator for low frequency operations

In this paper, a new active-only integrator which can be used to realize low frequency filters with small chip area is presented. The circuit can be effectively implemented using transconductance elements and its integration frequency is electronically controllable. In order to illustrate its usefulness, a second-order multifunction filter with low cut-off frequency, yet which occupy a small chip area is presented. Simulation results of the filter using SPECTRE in the CADENCE design tool which verify its proper operation are provided.

MOS-only biquads with extended operating frequency range

In this paper, a MOS-only multifunction filter which simultaneously realizes second-order lowpass and bandpass functions is presented. It is shown that the filter offers very useful advantages, such as low occupied chip area and suitability for high-frequency operation. Although the operation frequency range of the filter is found to be limited, a circuit design technique is proposed to remedy this issue. The validity of the theoretical discussions is verified by Spectre simulation results.

On the design and implementation of real active-only filters

In order to overcome some practical design and implementation issues of real active-only filters, a lossless integrator that employs one current controlled current conveyor and one voltage buffer with adjustable gain is presented. A real active-only filter circuit based on this integrator block is presented and designed. The feasibility of this filter in a 0.35μm CMOS process is verified through SPECTRE simulation program in the CADENCE design tool.