HP 8753E manual Processing Details

While only a single flow path is shown, two identical paths are available, corresponding to channel 1 and channel 2. When the channels are uncoupled, each channel is processed and controlled independently.

Data point definition: A “data point” or “point” is a single piece of data representing a measurement at a single stimulus value. Most data processing operations are performed point-by-point; some involve more than one point.

Sweep definition: A “sweep” is a series of consecutive data point measurements, taken over a sequence of stimulus values. A few data processing operations require that a full sweep

of data is available. The number of points per sweep can be defined by the user. The units of the stimulus values (such as power, frequency, and time) can change, depending on the sweep mode, although this does not generally affect the data processing path.

Processing Details

The ADC

The ADC (analog-to-digital converter) converts the R, A, and B inputs (already down-converted to a fixed low frequency IF) into digital words. (The AUX INPUT connector on the rear panel is a fourth input.) The ADC switches rapidly between these inputs, so they are converted nearly simultaneously.

lF Detection

This detection occurs in the digital hlter, which performs the discrete Fourier transform (DFT) on the digital words The samples are converted into complex number pairs (real plus imaginary, R + jX). The complex numbers represent both the magnitude and phase of the IF signaL If the AUX INPUT is selected, the imaginary part of the pair is set to zero. The DFT hlter shape can be altered by changing the IF bandwidth, which is a highly effective technique for noise reduction.

Ratio calculations

These calculations are performed if the selected measurement is a ratio of two inputs (for example, A/R or B/R). This is a complex divide operation. If the selected measurement is absolute (such as A or B), no calculations are performed. The R, A, and B values are also split into channel data at this point.

Sampler/IF Correction

The next digital processing technique used is sampler/IF correction. This process digitally corrects for frequency response errors (both magnitude and phase, primarily sampler rolloff) in the analog down-conversion path.

Sweep-To-Sweep Averaging

Averaging is another noise reduction technique. This calculation involves taking the complex exponential average of several consecutive sweeps. This technique cannot be used with single-input measurements.

Application and Operation Concepts 6-6