| 摘要 |
PURPOSE:To make a filter incorporated with IC by changing the variance of a filter consisting of a resistance and a coupling capacitance, to the voltage applied to said capacitance, and absorbing the voltage in the IC. CONSTITUTION:The IC includes resistances 12 (resistance value; R1) and 19 (resistance value R2) and junction capacitors 13 (capacity value; C1) and 20 (capacity value; C2) and their relative ratios a=R2/R1 and b=C2/C1 are suppressed with high precision by paying attention to their layout. Consequently, the transfer function of the filter is expressed by 1/(1+SC1R1)(1+SabC1R1). Then, variance in time constant C1R1 is absorbed while the relative ratios (a) and (b) are held to obtain a high-precision secondary low-pass filter. For this purpose, the voltage of a power source 26 is varied to specify the capacities of the junction capacitors 13 and 20. The DC voltages of the junction capacitors 13 and 20 are nearly equalized by a buffer and DC level shifter 18 and their variation voltages are equal, so the relative ratio (b) is maintained even when the applied voltage is varied. |
