The effects of mismatch in Gm-C polyphase filters

Based upon state-space representation, the effects of component mismatch in a complex (or polyphase) Gm-C filter are examined. It was found that the effects of component mismatch in this kind of filter are twofold. The first is that it will distort the filter's frequency response. The second and probably more severe consequence is the crosstalk in which the unwanted image signal is leaked into the passband frequencies, interfering with the wanted signal of the selected channel. A simulation method of a polyphase filter is also presented, and simulation results based on Monte Carlo analysis are given.     

The effect of I/Q imbalance and complex filter component mismatch in low-IF receivers

In this paper, the effect of mismatch in the front-end section of the low intermediate-frequency (IF) receiver is investigated. In particular, the I/Q imbalance in quadrature mixing and component mismatch in complex filtering are concurrently taken into consideration. It is shown that the signal to interference ratio of the low-IF receiver cannot be generally improved by increasing the order of complex filter.     

Modular log-domain filters

A new modular approach for releasing log-domain filters is proposed. By using this approach, nonlinear Gm-C filter structures can be readily transformed into log-domain filters with linear transfer characteristics. The realisation of the log-domain integrator and biquad filters is demonstrated and the simulation results are presented     

Independent control of transconductance gain and input linear rangein a MOS linear transconductance amplifier

A linear self-biasing MOS transconductance amplifier is presented. A linear V-I transfer characteristic is obtained by square-rooting the drain current of a MOS transistor in the saturation region. The main advantage of the circuit is that its transconductance gain and input linear range can be adjusted independently. Simulation results are included to confirm the feasibility of the technique     

Instantaneous Companding Current-Mode Oscillator Based on Class AB Transconductor

A family of DC stable electronically tunable instantaneous companding integrators are presented. Based on these integrators, an electronically tunable oscillator is proposed. Since theoretically the integrators used in the proposed oscillator are inherently linear, they are capable of producing oscillating current signals with low THD levels.     

Design procedure for two-stage CMOS operational amplifiers employing current buffer

The design procedure of the two-stage CMOS operational amplifiers employing Miller capacitor in conjunction with the common-gate current buffer is presented. Unlike the previously reported design strategy of the opamp of this type, which results in the opamp with a pair of nondominant complex conjugate poles and a finite zero, the proposed procedure is based upon the design strategy that results in the opamp with only one dominant pole. Design example of the proposed procedure is given.     

Logarithmic data converter suitable for hearing aid applications

A novel method for analogue-to-digital conversion with compressive /spl mu/-law transfer characteristic, suitable for hearing aid applications, is presented. The proposed method can be realised as low-power tunable analogue-to-digital converters in both pipeline and algorithmic architectures and is integratable in CMOS technology.     

A Very High-Frequency Transistor-Only Linear Tunable Companding Current-Mode Integrator

A low-distortion tunable transistor-only integrator suitable for applications in the frequency range approaching the f _T of transistors is presented. The circuit is a modified version of the recently introduced companding current-mode integrator utilizing the non-linear base-emitter diffusion capacitance of the BJT. A first-order approximation of the circuit characteristics is explained, followed by a brief discussion on the departure from ideal characteristics due to transistor nonidealities. Experimental and simulated results of practical integrators are given to verify the feasibility of the proposed modified circuit.     

Instantaneous companding and expressing: a dual approach to linearintegrator synthesis

The authors draw together work on log-domain and companding integrators and show that from an implementation perspective, there actually exists four integrator types. The concept of instantaneous expressing as the antithesis of the recent instantaneous companding integrator is introduced and it is shown that theoretically, both integrators should result in the same linearisation. The discussion is appropriate to both BJT and MOS technology     

Selection of the common-mode feedback network connection of fully differential Gm-C filters

It is well known that fully differential (FD) structures have many advantages over their single-ended counterparts. However, the main disadvantage of FD circuit is the potential instability caused by the inherent common-mode (CM) positive feedback loop. To solve such an instability problem, extra common-mode feedback (CMFB) and/or common-mode feedforward (CMFF) circuitries are often incorporated to stabilise the circuits. We present a systematic method for checking the stability condition and identifying the most suitable CMFB network connection for a particular FD Gm-C filter. It has been demonstrated that the CMFB network connection that provides highest CM rejection is not necessarily the conventional arrangement commonly used in FD Gm-C design.