Ultralow-Power Synchronous Demodulation for Low-Level Sensor Signal Detection

Abstract

The design and experimental characterization of a high-resolution analog lock-in amplifier (LIA)-based measurement system is presented in this paper. Different design strategies are used to attain a versatile solution which features programmable gain (72.6 -82.6 dB) and operating frequency (5 -115 kHz), preserving good recovery performance. The prototype, integrated in the UMC 0.18 µm CMOS process with a single supply voltage of 1.8 V, achieves a resolution of 200 nV and a high dynamic reserve of 43.5 dB, showing significantly lower power consumption (885 µW) than high-resolution state-of-the-art LIAs with minimum size (0.075 mm 2 silicon area). To validate the amplitude recovery performance of the proposed single-phase LIA, it was used to measure the equivalent value of a passive resistive sensor, exhibiting a maximum error of 1.9 % when RS is varied from 100 Ω to 10 kΩ with an input signal in the order of hundreds of microvolts. Thus, it constitutes a highly suitable choice for portable and lab-on-a-chip sensing applications.

A CMOS Low Pass Filter for SoC Lock-in-Based Measurement Devices

“…Thus, there was an accuracy power–area trade-off that was dependent on the order of the filter. Thanks to the implementation of a fully integrated low pass filter, we achieved a completely integrated lock-in amplifier, together with the previously authors proposal [21] for a multichannel measurement device.…”

“…Different integrated LIAs have been recently proposed for smart instrumentation applications [13,19,20,21] to exploit the advantages that render CMOS compatibility in terms of miniaturization. However, these LIAs maintain the LPF external use of off-chip resistors and capacitors [19,20,21] or, for fully integrated LIA solutions [13], the active filter area is rather large (it is the dominant element of the 3.6 mm 2 area of the implemented chip) for frequencies ~300 Hz. In particular, a previous author’s proposal [21] achieves very competitive capabilities in terms of area, power, and signal recovery, but the LPF is also kept external.…”

“…However, these LIAs maintain the LPF external use of off-chip resistors and capacitors [19,20,21] or, for fully integrated LIA solutions [13], the active filter area is rather large (it is the dominant element of the 3.6 mm 2 area of the implemented chip) for frequencies ~300 Hz. In particular, a previous author’s proposal [21] achieves very competitive capabilities in terms of area, power, and signal recovery, but the LPF is also kept external. Thus, the purpose of this work was to design an LPF suitable for this LIA architecture to achieve a fully integrated design.…”

Low Cost Autonomous Lock-In Amplifier for Resistance/Capacitance Sensor Measurements

“…In fact, the LIA can be seen as a Band-Pass Filter with a very high quality factor Q = f 0 /f LP , where f 0 is the operating frequency and f LP is the LPF cutoff frequency, so it filters most of the noise contributions at frequencies different from that of the signal of interest. It has been chosen over other proposals of the authors [36,37] due to its good features in terms of input dynamic range, resolution, linearity, input referred noise, programmable gain, low power consumption and low integration area, which makes it a versatile and adaptable solution for different applications. Its main characteristics are summarized in Table 1.…”

“…However, if the sensor consists of a complex impedance, with both resistive and capacitive components, the system should be used as a dual-phase LIA where both outputs deliver the complete information of the sensor [26,27]. In this work, the proposed LIA system is characterized as a single-phase instrument with phase alignment for low-amplitude resistive and capacitive sensors measurements, since in previous works [33,36] the circuit noise immunity was already tested. The electrical equivalent of resistive and capacitive sensors was measured under controlled environmental conditions to eliminate any variation due to temperature, humidity, and light.…”