A low-voltage ultra-low-power translinear integrator for audio filter applications

Abstract

Abstract-In this paper, the design and measurement of a 1-V translinear integrator and its application in a controllable secondorder lowpass filter for hearing instruments is presented. A semicustom version of the filter has been integrated in a standard 2-m, 7-GHz, bipolar IC process and operates at voltages down to 1 V, consumes only 6 A, and has a dynamic range of 57 dB for a total harmonic distortion below 2%. Its cutoff frequency is linearly adjustable in octaves from 1.6 to 8 kHz.Index Terms-Active filters, bipolar analog integrated circuits, current mode, low power, low voltage.

A generalized class of dynamic translinear circuits

“…These capacitance currents are used to implement the derivatives _ I out and _ I x . We use (8) and (9) to obtain a circuit that is not a member of the class of ESS filters. These definitions are valid if Ix and Iout are class-A biased, i.e., if they are strictly positive.…”

“…The only aim here is to demonstrate the existence of a more general class of DTL circuits. Equation (8) for I C is implemented by Q 6 ; Q 7 , and C 1 . The collector currents of these two transistors are the state variables, i.e., I C; Q = I out and I C; Q = I x .…”

Synthesis of Log-Domain Filters from First-Order Building Blocks

“…Our work instead concentrates on the use of logdomain ®lters for audio-frequency applications [8,11,12], the use of current-mode ®ltering for current-mode applications, and the application of log-domain ®lters in system design [13]. The low frequency range of audio requires a large RC time constant, which for the log-domain ®lters described here is inversely proportional to the bias current I b .…”

A wide-tunable translinear second-order oscillator

“…If we assume that the oscillator current is sinusoidal, thus , osc , and osc follow from (11) and (12) being 2 / osc .…”

“…Although not recognized then, this was actually the first time a first-order linear differential equation was implemented using translinear circuit techniques. In 1990, Seevinck introduced a "companding current-mode integrator" [5], and since then the principle of translinear filtering has been extensively studied by Frey, see, e.g., [6], Punzenberger and Enz [7], Toumazou and Lande [8], Perry and Roberts [9], and Mulder and Serdijn, see, e.g., [10], [11].…”