KEYWORDS: Amplifiers, Signal detection, Sensors, Linear filtering, Optical amplifiers, Optoelectronics, Interference (communication), CMOS sensors, Signal to noise ratio, Phase shifts
We have designed dual lock-in amplifier (LIA) circuits in 0.18 μm CMOS technology for antibody-antigens
(IgG) detection using optoelectronics. The purpose of this work is to develop a lock-in amplifier integrated circuit (IC)
using the dual phase scheme that detect the phase difference between the input signal and the reference signal although a
phase shifter is absent. Our LIA consist of high gain amplifier, signal amplifier, and phase sensitive detection. Amplifier
structure is based on two-stage differential operational amplifier (op-amp) with RC Miller compensation technique. By
using the RC Miller compensation technique, we obtain 60° the phase margin of the op-amp. Here, the resistor works for
increasing the unit gain bandwidth and the capacitor works for increasing the phase margin. The lock-in amplifier
consume 8.6 mA from a 1.8 V supply.
KEYWORDS: Signal detection, Interference (communication), Linear filtering, Biosensors, Switches, Sensors, Modulation, Signal to noise ratio, Photodetectors, Amplifiers
Recently, a number of portable biosensors have been developed to check the health condition of human beings
regardless of time and place. Though those sensors have a merit of a handy one, the signals are inevitably measured with
intensive background noises. In order to detect a weak signal concealed in intensive background noises such as Johnson
noise, 1/f noise, and shot noise, a special technique is essentially required. As of a special technique, the lock-in
detection method is able to minimize the effects of these noises using modulated signal and reference signals. Previously,
we applied the lock-in detection method to infrared detection system. The sensitivity of this system was decided by the
1/f noise at the photodetector. In this work, we have demonstrated the portable bio-sensor system using high frequency
infrared laser diode and photodetector. Therefore, the main signal of interest may keep away from the effect of the 1/f
noise with hybrid-type highly sensitive lock-in detection module. This technique provides the minimum detection range
of 3 mV and the dynamic range of 25.8 dB at the noise level of 120 mV.
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