Nonlinearity of transistor capacitive frequency meter

Abstract

The amplitudes of these voltages are sufficient to provide a complete saturation of the blocked transistors. Let transistor T~ become conducting and transistor T 2 become blocked at a certain instant. Then, capacitor Ci, which was previously charged to voItage g 0, wilt discharge through the conducting transistor T 6 capacitor C~ will be charged up to voltage E 1 along the circuit consisting of the negative side of the supply source, the transistor T1, the capacitor C2, the resistance R, and the positive side of the supply source. In the next half period of the input voltage the capacitor C z will be charged and the capacitor C i discharged in the same manner. Thus, the charging current of the capacitors C 1 and C 2 will flow through resistance R twice in each period. Moreover, provided the values of the capacitors are equal, the mean charging currents of the two half period~ will also be equal. Therefore, it is possible to analyze the frequency meter's operation in any half period, and then simply double the quantitative expression obtained for the output voltage. In future we shall consider that C 1 = C~. = C. Let us examine the operation of the frequency meter in the half period when transistor T 2 begins to conduct and transistor T 1 is becoming blocked. Both transistors have a very low resistance ?'s in the saturated state and a very high resistance Rb in a blocked state. Moreover, the transition from one state to another requires a certain time, owing to the inertia of the transistors and the finite steepness of the switching pulse edges.