Rail-to-Rail Timer-Based Demodulator for AM Sensor Signals

Abstract

This paper proposes a novel timer-based demodulator for low-frequency amplitude-modulated (AM) sensor signals with a rail-to-rail operating range. The demodulator extracts the amplitude of the AM signal by measuring the period of a reference signal that is altered by the AM signal itself, as already suggested in a previous paper. The rail-to-rail operation, which is the main contribution of the novel circuit, is achieved by simply but cleverly incorporating a multiplexer that enables the comparison between the two signals (reference and AM) just at the beginning and at the end of the period measurement. This new topology offers an operating range that is up to more than four times wider than that reported in the literature. The input-output characteristic in such a wider operating range is not linear, but it can be accurately modelled by a second-degree polynomial.

Demodulating AM Square Signals via a Digital Timer for Sensor Applications

“…This paper, which continues and expands the work in [29], aims to prove that the timer-based demodulator proposed in Demodulating AM Square Signals via a Digital Timer for Sensor Applications Ferran Reverter and Manel Gasulla T [16], [17] is also valid for AM square signals, without requiring a rectifier/mixer, an LPF, or an ADC. The paper is organized as follows.…”

“…T Thanks to the MUX, the comparison between the triangular and AM signals is carried out just at the beginning and at the end of the period measurement. Any potential crossing between V1 and V2 from t1 to t2 does not affect the measurement, thus avoiding aberrant period readings and extending the operating range [17]. If the MUX was not moved to position "1" after t1, the comparison between V1 and V2 would have non-desired crossings at instants t4, t5, and t6 that would generate an aberrant value of T.…”

“…The circuit proposed herein and that employed in [17] are the same, but their operating conditions are completely different, as summarized in Table I. When the circuit in Fig.…”

“…A similar approach has also been proposed to measure sensors that provide a voltagemodulated output [14], [15], but this is assumed of very low frequency or quasi static. The only attempt to measure sinusoidal amplitude-modulated (AM) sensor signals, with a carrier frequency in the range of kilohertz, through a digital timer was suggested in [16] and then improved in [17]. Unlike conventional demodulation techniques [18], [19] that require a rectifier/mixer, a low-pass filter (LPF), and an ADC, the demodulator proposed in [16] extracts and digitizes the AMsignal amplitude mainly via a digital timer.…”

Using a Digital Timer to Demodulate AM Triangular Signals for Sensor Applications

“…A similar approach has also been suggested to measure sensors that provide a voltage-modulated output [8], [9], but this is assumed of very low frequency or quasi static. The measurement of amplitude-modulated (AM) signals, with a carrier frequency in the range of kilohertz, via a digital timer has also been recently proposed for sinusoidal [10], [11] and square [12], [13] carrier signals. Unlike what occurs in conventional demodulators [14], [15] that require a rectifier/mixer, a low-pass filter (LPF), and an ADC, the demodulator proposed in [10]- [13] extracts and digitizes the AM-signal amplitude mainly through a digital timer, thus resulting in a simple and low-cost design solution.…”