The Analog-to-Digital Converter

The analog-to-digital converter receives the FID signals in the form of electrical voltages and converts them into binary numbers proportional to... 

Dynamic range Range determined by the number of bits in the output of the analog-to-digital converter represents the ratio between the largest and smallest signals observable in the digitized spectrum. 

Fig. 4.12. The molecular ion peak of [60]fuUerene at different settings of the dwell time per data point of the analog-to-digital converter. At 1 ns per datapoint (1 GHz) the peaks are well resolved and resolution is limited by the analyzer, at 2 ns (500 MHz) some broadening occurs and at 10 ns (100 MHz) peak shapes are reduced to triangles.

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. 

Another part of the loop program ascertains how much solution is left in the pump. A voltage picked off a ten-turn potentiometer, which is coupled to the piston-drive screw with a timing belt, is fed to the analog-to-digital converter and is compared with the previously stored reading from the thumbwheel switch. 

The attenuation of the optical signal by a monolayer is small and the upper limit on S/N is usually determined by the dynamic range of the analog-to-digital converters (ADC) (9). A simple method to diminish the ADC limitation, and improve the S/N ratio would be to increase the amount of sample probed by the beam. Since the ADC peak-to-peak noise level for a single scan is -10-3 absorbance it may be necessary to average several... 

The second hardware unit was an interrupt, skip-check control unit for the Reticon arrays. This unit allows the computer to see the end-of-scan and beginning-of-scan pulses generated by the arrays and allows the computer to have an on/off control of the external clock which is used to start the analog to digital converter. 

Acquisition simply turn on the analog-to-digital converter and record a 1H FID. Fourier transformation of this signal will give an antiphase doublet whose amplitude is modulated by a factor cos( 2c t ). 

As discussed in Sec. 9.9, the backbone of an MCA is the analog-to-digital converter (ADC), the unit that digitizes the input pulse height and assigns it to a specific channel. Many types of ADCs have been developed, but the most frequently used is the Wilkinson type. ... 

The amplified TAC signal is fed to the Analog-to Digital Converter, ADC. The output of the ADC is the digital equivalent of the photon deteetion time. The ADC must work with an extremely high precision. Not only must it resolve the amplified TAC signal into thousands of time ehannels, but the time ehannels must also have the same width. Any nonuniformity of the channel width results in a systematie variation of the numbers of photons in the ehannels, creating noise or curve distortion. 

We can control both the width and the location of the SW. The width is controlled by varying the sampling rate of the analog-to-digital converter (A/D). We can translate (move side to side) the center of the spectral window by varying the transmitter frequency. The transmitter frequency is also known as the transmitter offset or the carrier frequency, or sometimes simply the transmitter (this is an imprecise term and should be avoided unless the context is well understood). On a Bruker instrument, the transmitter frequency is determined by a coarse value listed in MHz (sfrq, for spectrometer frequency)... 

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