Data Acquisition and Signal Processing for Smart Sensors

5

ADVANCED AND SELF-ADAPTING METHODS OF FREQUENCY-TO-CODE CONVERSION

In spite of the fact that today frequency can be measured by the most precise methods by comparison with other physical quantities, precise frequency-to-code conversion with the constant quantization error in a wide specified measuring frequency range (from 0.01 Hz up to some MHz) and with non-redundant conversion time can only be realized based on novel measurement methods for frequency-time parameters of the electric signal. This requires additional hardware costs and arithmetic operations: multiplication and division for calculations of the final result of conversion. Therefore, additional measuring (conversion) devices should be included in the microsystem. These include two or more multidigital binary counters, the multiplier and the code divider, logic elements, etc. Different design approaches are used. In the authors’ opinion, a successful solution is the use of a microcontroller core in such microsystems. In this case, with the aim to minimize the built-in hardware, it is expedient to take advantage of the program-oriented methods of measurement developed for frequency-time parameters of signals.

5.1 Ratiometric Counting Method

We shall first consider the idea of the original method of the discrete count [98,117], called the ratiometric counting method, which allows frequency-to-code conversion with a small constant error in a wide frequency range, we shall then consider how this method can be realized. ...