Inductorless variable equalizers using feedback and feedforward

Inductorless variable equalizers using networks with feedback and feedforward are investigated. They comprise two shaping networks, two adders, and a single variable gain element. They work over a full variation range and the variable element can share a common grounded terminal. The design of the variable characteristics is quite straightforward compared with conventional types. Equalization errors caused by component imperfection in this type of variable equalizer are analyzed and compensation methods for these errors are investigated. Some practical examples are given that prove the efficiency of the error compensation and the feasibility of this type of variable equalizer. Variable equalizers with high-input and low-output impedances using three or four transistors are illustrated. Owing to their simple structures and weak feedback and feedforward, they can be used in video or higher frequency bands. Experiments using transistors with an
f_{\tau}
of I GHz were performed over a ± 7-dB variation range and a bandwidth of 20 MHz.