Analog lock-in amplifiers

G. Ferri, P.D. Laurentiis, A. D Amico and C.D. Natale, A low-voltage integrated CMOS analog lock-in amplifier prototype for LAPS applications, Sens. Actuators A Phys., 92(1-3) (2001) 263-272. 

Analog lock-in amplifiers have a practical lower frequency limit of about 1 Hz, owing to the necessity of AC coupled inputs. Because any DC signal will influence the results, the method requires pure AC signals. The upper frequency limit of the analog lock-in technique is typically about 100 kHz to 1 MHz, and is mainly due to problems of stray capacitance. The dynamic range can reach over 100 dB. 

The output of the lock-in amplifier is input to a sample-and-hold amplifier or directly to the analog-to-digital converter. This signal is converted to a digital and thus machine-readable form. 

The second approach is to send the signal to analog, phase sensitive detectors, or lock-in amplifiers, that will analyze the harmonic content. The DC component, in turn,... 

In this scheme, analog Fourier decomposition of the signal using lock-in amplifiers becomes impractical and a digital fast Fourier transformation is preferred. Such an analysis would lead to 22 linear combinations of the 16 Mueller matrix components of the sample. This is an overspecified system, and the extra information can be used as either an internal check of consistency or discarded. It is important to make proper choices of the angular velocities, and D2. Clearly, these frequencies cannot be simple multiplies of one... 

Figure 8.27 On-chip current mode lock-in amplifier. VCC voltage to current converter, CCC = current to current converter, ADC = analog to digital converter...

In the analog detection of CPL, the differential emission intensity, A I, is assumed to be proportional to the output of the lock-in amplifier, and the total emission intensity, /, is proportional to a DC output voltage. These are generally independent measurements, so that a... 

In numerous methods in which the in-phase and out-of-phase signals are recorded using a lock-in amplifier or analogous instruments, it is customary to represent results in a graph where Sy is plotted vs S. Depending on the application, these plots are called parametric plots, complex plane plots, Argand diagrams, Nyquist plots, and Cole-Cole plots. In these plots frequency co is an implicit parameter. 

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