| 摘要 |
<p>A magnetic reproducing head amplifier according to the present invention comprises a differential amplifier (3) referred to as one of these three types: a balanced input type, a balanced output type, or a balanced input/ouput type. The amplifier comprises at least one positive feedback circuit (10) for passing a positive feedback current to the differential amplifier and at least one negative feedback circuits (11) for passing a negative feedback current to the same, and is configured so that a positive feedback and a negative feedback are simultaneously performed by the positive feedback circuit as well as the negative feedback circuit. A resonance peak characteristic at the input part of the differential amplifier is dumped by the negative feedback current, and therefore a frequency characteristic as well as a group delay characteristic of the output of the differential amplifier becomes flattened. Moreover, the use of the positive feedback current from the positive feedback circuit permits the charging current from the signal source to the input capacitance of the differential amplifier to be reduced, that is to say, an effective input capacitance is reduced, and thereby a resonance frequency at the input part of the differential amplifier can be shifted to the vicinity of the upper limit of the transmission band. Consequently, a stable amplification operation can be achieved for FM carriers for carrying wide frequency signals, such as HDTV signals.</p> |
