Phase frequency detector

PLL-based oscillators are characterized by a loop with phase detection of two signals in a sensor and reference path. A circuit based on a phase-locked loop (PLL) configuration has been introduced in [46]. The core of this solution is a sensor circuit consisting of a reference and a sensor path. It is essential for the working principle to maintain an identical structure in the sensor and the reference path, in order to minimize systematic differences between them. A phase frequency detector measures the phase difference between the sensor and reference path. An adjustable capacitance in the reference path allows for Co-compensation. The oscillator can therefore work at/s. 

The amplified signal is passed to a double-balanced mixer configured as a phase-sensitive detector where the two inputs are the NMR signal (cOq) and the frequency of the synthesizer (03. gf) with the output proportional to cos(coq - co gj.)t + 0) + cos((coq + + 9). The sum frequency is much larger than the total bandwidth of the... 

Theory. If two or more fluorophores with different emission lifetimes contribute to the same broad, unresolved emission spectrum, their separate emission spectra often can be resolved by the technique of phase-resolved fluorometry. In this method the excitation light is modulated sinusoidally, usually in the radio-frequency range, and the emission is analyzed with a phase sensitive detector. The emission appears as a sinusoidally modulated signal, shifted in phase from the excitation modulation and partially demodulated by an amount dependent on the lifetime of the fluorophore excited state (5, Chapter 4). The detector phase can be adjusted to be exactly out-of-phase with the emission from any one fluorophore, so that the contribution to the total spectrum from that fluorophore is suppressed. For a sample with two fluorophores, suppressing the emission from one fluorophore leaves a spectrum caused only by the other, which then can be directly recorded. With more than two flurophores the problem is more complicated but a number of techniques for deconvoluting the complex emission curve have been developed making use of several modulation frequencies and measurement phase angles (79). 

The impedance can be measured in two ways. Figure 5.23 shows an impedance bridge adapted for measuring the electrode impedance in a potentiostatic circuit. This device yields results that can be evaluated up to a frequency of 30 kHz. It is also useful for measuring the differential capacity of the electrode (Section 4.4). A phase-sensitive detector provides better results and yields (mostly automatically) the current amplitude and the phase angle directly without compensation. 

The measurement of the Stark effect were carried out with the electric-field modulation technique at room temp, in vacuo (about 10 3 torr). A sinusoidal ac voltage (500 Hz) was applied between the A1 electrodes. Then, the change in transmittance induced by the applied electric field were measured with a phase-sensitive detector (NF Electronic Instruments LI-575A) at the fundamental frequency. 

When a component of the modulated absorption wave which synchronizes with the fcth harmonic of the modulation frequency is detected by a phase-sensitive detector, the signal obtained is proportional to the coefficient of the kih term ak (// ). 

The real and imaginary spectra obtained by Fourier transformation of FID signals are usually mixtures of the absorption and dispersion modes as shown in Fig. 2.13 (a). These phase errors mainly arise from frequency-independent maladjustments of the phase sensitive detector and from frequency-dependent factors such as the finite length of rf pulses, delays in the start of data acquisition, and phase shifts induced by filtering frequencies outside the spectral width A. 

The experimental set-up for femtosecond hyper-Rayleigh scattering is in essence identical to the one for the nanosecond experiments.9 Only the gated integrators for the nanosecond measurements are replaced by a chopper and a phase-sensitive detector in the high-frequency femtosecond experiment. 

One excellent way to increase the S/N ratio is to tune the detector to the exact same frequency v as the source (using a lock-in amplifier, also known as a phase-sensitive detector or as homodyne detection) and also to discriminate the phase

rc/2 or (3/2)n. This can be used to discriminate up to 60 dB. 

The key element of this amplifier is a phase sensitive detector. It demodulates the frequency of interest and produces a signal, which is a function of the phase angle of the input signal. The input circuit of a lock-in amplifier is properly adjusted to achieve the ability of the devise to recover signals that are overloaded with -> noise. 

The use of a phase-sensitive detector to demodulate the f.i.d. signal emerging from the receiver coil is equivalent to providing a rotating frame of reference for the spectrometer itself, as the detector is referenced to the constant carrier r.f. (ft). The f.i.d. signal detected, therefore, contains only phase and intensity information for the difference frequency between the carrier frequency applied and the... 

FIGURE 3.6 (a) Depiction of magnetization M precessing in the rotating frame at the frequencies indicated. W/2 is the Nyquist frequency, and sampling of both phase-sensitive detectors is illustrated at t- /W and 2/ H7to obtain projections along both x and y. ... 

FIGURE 3.6 (Continued) (b) Example of foldover of frequencies above the Nyquist frequency with two phase-sensitive detectors. The lower spectrum (spectral width 5000 Hz) faithfully reproduces the true spectrum, but the upper spectrum (spectral width 3600 Hz) shows that peaks near + 2000 Hz now display an aliased frequency near — 1800 Hz and appear near the right-hand end of the spectrum. Sample D-glucorono-6,3-lactone-l,2-acetonide in DMSO-<4 at 500 MHz. Spectra courtesy of Joseph J. Barchi (National Institutes of Health). 

If the phase-sensitive detectors are adjusted to give a phase angle (Eq. 3.8) ( — 4>r ) = 0, the real part of the FT spectrum corresponds to pure absorption at the pulse frequency, but off-resonance lines display phase angles proportional to their off-resonance frequency as a consequence of limited rf power and nonzero pulse width (Eq. 2.55). However, acquisition of data as complex numbers from the two phase-sensitive detectors and subsequent processing with a complex Fourier transform permit us to obtain a spectrum that represents a pure absorption mode. 

The criteria for SHAC voltammograms to yield reversible potentials are that the zero-current crossing potentials must be both frequency- and phase-independent. In practice one measures the in phase (/) and quadrature (Q) components of the second harmonic a.c. current by means of a phase-sensitive detector or lock-in amplifier. The response is illustrated in Figs 10-12 obtained during measurements on the oxidation of 9,10-diphenylanthracene (DPA) in acetonitrile (Fig. 10) and in acetonitrile containing pyridine (Figs... 

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