| 摘要 |
An improved servo demodulator channel employing a transconductance balanced modulator as a polarity switch, an AGC amplifier and a signal separation circuit. A transconductance balanced modulator comprises two amplification transistors and four output transistors which together form two signal channels, each comprised of an amplification transistor connected in parallel to two output transistors. In a specific embodiment, the transistors are n-p-n transistors, the emitters of the two output transistors associated with a given channel being connected to the collector of the amplification transistor. The transconductance balanced modulator is configured so that the two amplification transistors are interconnected as a differential amplifier, and the base electrode of an output transistor in one signal channel is connected to the base electrode of an output transistor in the other signal channel, the base electrodes of the other two output transistors also being interconnected. Each interconnected pair of base electrodes is connected to a control signal terminal pair. The invention discloses a means whereby a transconductance balanced modulator configured as above-described can be operated as a polarity switch, an AGC amplifier and a signal separation circuit in a servo preamplifier and demodulator chain for use in magnetic disk head positioning systems.
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