Albert C. van der Woerd

Design principles for low-voltage low-power analog integrated circuits

In this paper it is argued that there are good reasons to choose current as the information-carrying quantity in the case of low-voltage low-power design constraints. This paper focuses on the influence of the transfer quality on that choice. To obtain power-efficient transfer quality, indirect feedback is shown to be a good alternative to traditional feedback techniques.

A 1-V Class-AB Translinear Integrator for Filter Applications

In this paper, the design and measurements of a 1-volt class-AB instantaneous companding translinear integrator are presented. The use of instantaneous companding and class-AB operation gives an improvement of the dynamic range and a reduction of the power consumption. The proposed circuit uses only bipolar transistors and one capacitor and is, therefore, very well suited for integrated implementation. Its unity-gain frequency can easily be controlled by a current. Simulations and measurements of a semicustom realization, to be applied in a hearing instrument, confirm correct operation of the designed circuit. The translinear integrator operates from a single supply voltage down to 0.95 V. The current consumption is less than 1.9 μA for an input current of 180 nA (p). The dynamic range is better than 73 dB over a bandwidth of 8 kHz.

Analog circuits for a single-chip infrared controlled hearing aid

All analog circuits for a remotely controllable subminiature hearing aid are presented. It is feasible to integrate all circuits together with an I2L decoder on a single bipolar chip. The volume level and the cutoff frequency of a high-pass filter can be controlled. Besides, the device can be remotely switched at microphone and telephone coil, and switched into a standby mode. All circuits presented have been tested with a semicustom realization.

Low-voltage low-power full-integratable automatic gain controls

This paper discusses the design of low-voltage low-power fully-integratable automatic gain controls. Four different AGCs are presented, all consisting of three elementary building blocks: a controlled amplifier, a comparator and a voltage follower. Their design is treated separately. As an example, the final section describes an automatic gain control for hearing instruments, realized in a bipolar process.

Design rules for an integratable low-power amplifier/filter combination

In this paper design rules for a circuit topology in which there is an inseparable combination of an amplifier and a filter characteristic, are presented. By intentionally using the capacitance of an already present input sensor for the filtering, the total required integrated capacitance is much less than that in circuits, which have a separately designed amplifier and filter function. Consequently, it is possible to have the advantage of a better integratability. Moreover, less complexity in the design is achieved. The presented circuit shows a current-to-voltage conversion and an inherently controllable second-order low-pass filter characteristic. A discrete realization has been designed to test the circuit. This circuit operates down to a 1 V supply voltage and the transfer shows a 1.8 MΩ currentto-voltage conversion with a bandwidth of 6 kHz. Measurement results of this circuit show that a 63 dB dynamic range can be achieved with a total required integrated capacitance of only 31 pF.

Biasing a differential pair in low-voltage analog circuits: a systematic approach

This paper deals with a systematic approach to the common mode and the differential mode biasing of a differential transistor pair. Four different variants will be shown, two of these variants show practical importance; a practical circuit of one of these variants turns out to be the traditional “long-tailed pair.” This variant is mainly suited, if the input signal operates at “voltage level,” whereas another variant has great advantages if operation at “current level” occurs. Besides, the latter variant turns out to be very favorable in circuits operating with a single low supply voltage. Two practical circuits based on this variant are given.

Highly efficient micro-power converter between a solar cell and a rechargeable lithium-ion battery

This paper describes the design of a low-power photo-voltaic power converter which will be used in a directional hearing aid. It is argued, that the use of a switched-capacitor converter is needed when integration on a chip is demanded. This converter combined with a parallel power converter has an efficiency that lies between 70% and 85%. This efficiency depends on the charging voltage of the implemented rechargeable thin-film lithium-ion battery. This battery will be glued at the back side of the power-converter chip. The converter is controlled by a maximum-power-point-tracker to perform maximum charging of the battery under the varying conditions of the solar cell. The controller is adapted to operate with a switched-capacitor converter. This paper also shows a structured derivation of the necessary solar cell area. The complete power converter has been designed in a custom CMOS process and the major part of the circuit operates in the sub-threshold area.

Voltage-translinear circuits

TransLinear (TL) circuits are based on the exponential law describing the bipolar transistor. Based on the square law model for the strong inversion MOS transistor, a different type of TL circuits can be realised [67-70]. The formal definition of the general principle behind these ‘Voltage-TransLinear’1 (VTL) circuits was published by Seevinck and Wiegerink in [67], see Section 2.3.

Device non-idealities

The analysis and synthesis methods discussed in the previous chapters are based on the exact exponential behaviour of the circuit elements. Nonetheless, many second-order effects influence the accuracy of a TransLinear (TL) circuit and in general result in distortion. Fortunately, many techniques have been developed in the past to overcome these problems. For example, this is demonstrated by the TL multiplier reported in [49], which provides a total harmonic distortion level of-95 dB.

Analysis of translinear circuits

Although synthesis is more powerful than analysis, it must go together with a generally applicable analysis method in the same domain. This is a prerequisite for structured electronic design. This chapter therefore explores the possible analysis procedures that can be applied to investigate the behaviour of Static TransLinear (STL) and Dynamic TransLinear (DTL) circuits, before synthesis methodologies are surveyed in Chapter 4.