Abstract: A differential amplifier (24) includes a pair of transistors (Q2 and Q9); a differential amplifier 25 includes a pair of transistors (Q3 and Q6). A difference in output currents at the differential amplifier (24) is detected by differential amplifier (25). Then, transistors (Q3 and Q6) in differential amplifier (25) supply currents flowing therein into transistors (Q4 and Q5), whose bases are connected to each other via a capacitor (26). With this arrangement, a difference in DC components between a pair of differential currents flowing in the differential amplifier (25) is obtained at both terminals of the capacitor (26). The obtained voltages at the both terminals of the capacitor (26) are fed back to the input of the differential amplifier (24) via transistors (Q1 and Q8), so that offsets at inputs of the differential amplifier (24) are corrected.

Abstract: A video signal is read from a magnetic tape, and amplified by a head amplifier. The video signal then passes separately through first and second BPFs, the BPFs having respective passband characteristics so as to be applied to a first adding circuit. A first coefficient circuit multiplies the output from the first BPF by a positive coefficient while a second coefficient circuit multiplies the output from the second BPF by a negative coefficient. A second adding circuit adds all three signals, namely, signals from the first adding circuit and from the first and second coefficient circuits, and outputs the added signal to a trap circuit. The frequency characteristic of the equalizer can be adjusted by changing the coefficients in the first and second coefficients circuits. A change of the coefficients does not affect the level of the carrier component of a luminance signal.

Abstract: A drop out compensation circuit for resolving the unnaturalness of the pictorial image due to a long period drop out compensation is disclosed. This drop out compensation circuit comprises a drop out detecting circuit, a delay circuit for delaying a drop out detected output, and a circuit for limiting the drop out compensation to the delay time period by the delay circuit in response to the drop out detected output and the delay signal of the delay circuit. Accordingly, the drop out compensation is performed only within a range wherein it is visually natural, so that unnatural pictorial image does not appear.

Abstract: A head amplifier is integrated into an IC with a minimum number of pins and outside parts as well. An offset cancellation circuit cancels offset voltages to prevent distortion of playback signals. An amplifier amplifies a playback signal to produce an output signal that is fed to one input of a differential amplifier. A reference voltage is fed to the second input of the differential amplifier. The input of the differential amplifier is compared in a comparator with the reference voltage to produce a feedback signal for cancelling offset voltages. The feedback path is frequency sensitive to reduce frequency response at low frequencies, and to compensate for distortions produced at high frequencies from using PNP transistors in the comparator.