Log-domain Filters Research Articles

A compact low-power BiCMOS log-domain filter

A third-order Chebyshev filter based on the log-domain principle and integrated in a 1-/spl mu/m BiCMOS process is presented. It has a nominal cutoff frequency of 320 kHz corresponding to a bias current of 1 /spl mu/A, and can be frequency tuned over almost three decades up to about 10 MHz. It operates with a nominal supply voltage of 1.2 V, maintaining a dynamic range (DR) at 1% THD of 57 dB. For cutoff frequencies in the range of 10 kHz, the supply voltage can be reduced down to 0.9 V. The filter occupies an active area of 0.25 mm/sup 2/ and dissipates 23 /spl mu/W, corresponding to a power consumption per pole and edge frequency of only 24 pJ. These results demonstrate the potential of log-domain filters for very low-voltage and low-power applications.

Analogue micropowered log-domain tone controllerfor auditory prostheses

A micropower tone-control circuit comprising two first-order log-domain filters and a subtractor built with MOS transistors in weak inversion is described. The tone-controller is capable of providing bass cut/boost and treble cut operations. This circuit is being used in new designs of a conventional (acoustic) hearing-aid and cochlear implant.

Log-domain synthesis of an nth-order filter

A synthesis approach for a nth-order log-domain filter is proposed. Using the logexponential relation between current and voltage of a bipolar junction transistor (BJT) or MOS transistors operating in weak inversion, a circuit transformation from log-domain to linear OTA-C filters is developed. Based on the simulation of a signal-flow-graph on the nth-order transfer function, the realization of the highorder log-domain filter is presented. A 4th-order low-pass filter is designed and simulated in HSPICE.

State-space synthesis and analysis of log-domain filters

The general state-space synthesis of linear filters is reviewed including the use of linear transformations. Then the use of time-varying nonlinear mappings on the state variables is shown to produce equations for the synthesis of linear, linear companding, and log-domain filters. Formulas are developed which underlie the realization of log-domain filters. Design issues relating to realizability, noise, and nonideal performance are discussed using the state-space mathematical formulation.

Very high-frequency log-domain bandpass filters

A transistor-level all n-p-n differential log-domain integrator geared toward low-distortion very high-frequency (VHF) applications is proposed. Systematic design steps are suggested and used to realize second and higher order balanced bandpass filters, based on the method of operational simulation of doubly-terminated LC ladders. We discuss the special sensitivity of log-domain integrators to small dc biasing offsets, practical issues in the design of the input and output interface stages, and the effect of parasitic resistors and capacitors on high-frequency log-domain filters. Experimental results from a 0.8-/spl mu/m BiCMOS implementation of a single-ended 220-MHz biquad and a balanced 130-MHz fourth-order bandpass filter are reported, with emphasis on their distortion characteristics.

A 3.3 V Current-Controlled √ -Domain Oscillator

In this paper, the strong inversion MOS analog of the recently proposed class of log-domain filters, or translinear filters, is proposed.The dynamic √ -domain principle, or dynamic voltage-translinear principle, exploits the quadratic law, describing the MOS transistor in the strong inversion region, both to perform an expanding V-I conversion of the capacitor voltages and to implement multiplications and square roots of currents based on the voltage-translinear principle.The presented theory is applied to the design of a current-controlled two-integrator oscillator. Experiment results of a pure CMOS test IC show the feasibility of the √ -domain principle. The realized oscillator has a THD of −42 dB and is linearly frequency tunable across 1.3 decades.

Syllabically compandinglog domain filter usingdynamic biasing

It is shown that syllabic companding in a log domain filter can be accomplished by varying the bias currents, thus eliminating the need for separate compressor and expander blocks. The advantages of the proposed technique are discussed.

Modular log-domain filters

A new modular approach for realising 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 presented.

A 1.2-V low-power BiCMOS class AB log-domain filter

A third-order class AB current-mode Chebyshev filter based on the log-domain instantaneous companding principle and integrated in a 1-/spl mu/m BiCMOS process is presented. It has a nominal cutoff frequency of 320 kHz corresponding to a bias current of 1 /spl mu/A and can be frequency tuned over almost three decades up to about 10 MHz. It operates with a nominal supply voltage of 1.2 V maintaining a dynamic range at 1% total harmonic distortion (THD) of 65 dB. For cutoff frequencies in the range of 10 kHz, the supply voltage can be reduced down to 0.9 V. Typical to companding systems, the class AB filter shows a measured SNR versus input signal that saturates to a maximum value which for this particular realization is 52.5 dB. It has an active area of 0.55 mm/sup 2/ and dissipates 65 /spl mu/W, leading to a power consumption per pole and edge frequency of 67.7 pJ. These results demonstrate the potential of instantaneous companding filters for very low-voltage and low-power applications with moderate linearity and SNR requirements.

Table-based log-domain linear transformation filter

A design table for realising log-domain linear transformation filters is presented. Based on this design table, doubly terminated LC ladder filters with or without finite transmission zeros can be efficiently synthesised. Moreover, two design procedures are also given. A canonical log-domain elliptic ladder filter can be realised using one of these procedures. Simulation results are given to verify the theoretical analysis.

Log domain filtering for RF applications

A new second-order log filter topology, which is particularly useful for RF signal processing, is introduced with a discussion of how its features meet the needs of RF design. The design concept behind log filters is reviewed. Simulation and experimental results on a test IC are presented for an electronically tunable filter which operates beyond 400 MHz, with Q's in excess of 60, using the AT&T CBIC-V2 process.

The design of log-domain filters based on the operational simulation of LC ladders

A technique for the design of log-domain filters is introduced which is based on the operational simulation of LC ladders. The method is used to design a fifth-order Chebyshev and elliptic filter. HSPICE simulation results and experimental results are shown with emphasis on frequency behavior and linearity. The filters showed good correlation between the original filter specifications and the measured frequency response. They proved to be easily tunable and could be operated up to 1 MHz or one tenth of the f/sub T/ of the slowest transistor. Total harmonic distortion and intermodulation distortion was measured with results up to -47 and -55 dB, respectively.

State-space synthesis of log-domain oscillators

A state-space synthesis of oscillators based on log compression is presented. The approach is an extension of the recently proposed current-mode log domain filter synthesis methodology. Both simulated and measured results demonstrate that very low distortion oscillators can be synthesised at several megahertz using simple processing building blocks and off-the-shelf transistor arrays.

Micropower log-domain filter for electronic cochlea

A new approach to the design of a low-power cascadable analogue filter for applications such as silicon cochlea implants is described. One section of a possible silicon cochlea based on a second-order continuous-time filter employing MOS technology operating in weak inversion is presented. The idea is based on the recently proposed log-domain filter approach used previously in bipolar technology.

Log-domain filtering: an approach to current-mode filtering

A novel approach to filter design, based on Adams' [1] ‘log-domain’ filters, is proposed that yields a truly current-mode circuit realisation. Adams' idea, which was introduced in a limited context, is generalised to permit a complete distortionless synthesis procedure, which results in circuit implementations readily realisable using complementary bipolar processes. It is shown that, by introducing an exponential map on the state-space description of the desired linear system, a log-domain filter can be fully realised with transistors configured in current mirror-type groupings, current sources and capacitors. Owing to the mapping, the state variables are intrinsically related to current, and not voltage, in the resulting circuits, a fact that emphasises the current-mode nature of the design. A general biquadratic filter section is designed, and, following discussion of cascading sections, a seventh-order Chebychev lowpass filter is designed. All designed circuits are shown to be tunable over a two-decade range in frequency while their characteristics are accurately preserved, even for biquad sections whose f0Q product is greater than fT/10. The Chebychev filter is shown in simulation to possess nearly 60 dB dynamic range relative to 0.9% THD, with a cutoff frequency of nearly 5 MHz, using transistor models from AT&T's CBIC-R 300 MHz complementary bipolar process.