| 摘要 |
PURPOSE:To obtain a variable time constant circuit which is stable to temperatures by supplying the input to two current output circuits having the same temperature characteristics and different threshold levels and connecting the outputs of two time constant circuits which are charged and discharged with the output of each of said two current output circuits. CONSTITUTION:A current mirror circuit 22 contains an input terminal 21 and transistors TR24 and 25 which deliver the same current. While, TR34 and 37 hold points E1 and E2 at a fixed potential respectively by constant current sources 33 and 32 and resistances 35 and 38. In this case, it is possible to set the difference of potential between the points E1 and E2 at an optional value in response to the resistance value. Therefore the potentials are different between points P and Q when a current equal to the input current flows to resistances 31 and 33. For instance, if the potential of the point E1 is higher than that of the point E2, the signal is transmitted only to a terminal 51 of a time constant circuit 50 when the input signal is on a small level. While the signal is transmitted to both terminals 51 and 52 when the level of the input signal is sufficiently high. The time constant can be varied in response to the level of the input signal. In addition, the temperature changes are cancelled for both circuits. |
