A realization of monolithic variable integrators and their application to automatically tunable high‐frequency active filters

Abstract

AbstractWith the widespread use of home video and other equipment, it is strongly desired to realize a high‐frequency monolithic IC active RC filter. This paper proposes a method of constructing the integrator with voltage‐controlled current source operated by a single 5‐V supply. Even though operated by a single 5‐V supply, the proposed integrator can realize a wide dynamic range due to an elaboration in the output circuit. For a cutoff frequency of 1 MHz, the maximum input voltage for distortionless output voltage is 1.0 VP‐P. By a simple compensation, an excellent high‐frequency characteristic exceeding 2 MHz is obtained. The proposed integrator is of a variable characteristic with differential inputs, and, consequently, an automatically tunable leapfrog‐type filter can be realized. To evaluate the performance of the proposed integrator, a high‐frequency analysis and a computer simulation were made. The integrator was realized as a monolithic IC by the general‐purpose process for home‐use equipment, and the automatically tunable filter was constructed. The experimental result agreed well with the theory, indicating that the whole filter can be realized by a monolithic IC.