THERMOCOMPENSATED DC SOURCES FOR CURRENT-MODE DIGITAL-ANALOG CONVERTERS

Abstract

Sources of the reference voltage and current are the integral component of any electronic circuit. Especially important role sources of reference voltage and current play in analog circuits, many quantitative parameters of circuits operation depend on them. For instance, in analog-to-digital and digital-to-analog converters value of the full scale is determined by the reference source of voltage. Nowadays there exist many different approaches to the construction of D. C. sources circuits. Classic variant of reference voltage sources construction is the usage of the stabilitron and effects of Zener (tunnel) and avalanche breakdowns in it at the reverse-bias voltage. Zener breakdown occurs at the voltage of less than five volts and has negative temperature coefficient, avalanche breakdown occurs at higher voltages and has positive temperature coefficient. At the breakdown voltage in the range of five to eight volts its total positive voltage temperature coefficient (VTC) approximately equals negative voltage temperature coefficient (VTC) of the direct-biased diode. Sources of the reference voltage are determined by the bandgap voltage of the silicon, and provide good VTC at low supply voltages. To achieve thermal compensation in the circuit the matched transistors with the difference of the currents density , flowing across them, are used . Method of the reference voltage formation of the bandgap is attractive for the realization due to the comparative simplicity and low level of noise.The paper suggests new approach to the construction of the thermostable sources of the reference current on the base of the bipolar transistors using the voltage of the semiconductor bandgap and current mirrors. The given research contains circuit engineering analysis of the static characteristics of the proposed circuits of the thermocompensated bipolar DC sources of the circular type in the preset temperature range, principle of achieving thermal compensation are analyzed. Computer simulation of the static characteristics of the given reference current generators, such as current temperature drift as well as stabilization coefficient in case of the supply voltage change (loading capacity) is performed.