Data storage device with BiCMOS impedance-matched amplifier with transducer-bias

A data storage device comprising:

• a magnetic media;
• a recording head comprising a read transducer configured to generate a differential read signal in response to magnetic bit transitions on the magnetic media;
• and
• an amplifier coupled to the recording head via a transmission line and comprising:
• a first pair of bipolar junction transistors (BJTs), wherein bases of the first pair of BJTs define input nodes configured to receive the differential read signal from the read transducer via the transmission line;
• a second pair of BJTs, wherein bases of the second pair of BJTs are coupled to a bias voltage source, emitters of the second pair of BJTs are coupled to emitters of the first pair of BJTs, and collectors of the second pair of BJTs are cross-coupled to collectors of the first pair of BJTs to define output nodes at which a differential output signal of the amplifier is formed;
• a feedback resistor and an emitter follower coupled between the output nodes and the input nodes, wherein an input impedance of the amplifier is tuned by the feedback resistor;
• and
• a common-mode biasing circuit comprising an operational transconductance amplifier (OTA) configured to compare a common-mode input voltage of the input nodes to a reference voltage and to drive a pair of common-mode current sources coupled to the input nodes to regulate the common-mode input voltage.

A method for amplifying a differential read signal generated across a read transducer of a data storage device, the method comprising:

• applying the differential read signal across input nodes defined by bases of a first pair of bipolar junction transistors (BJTs);
• amplifying the differential read signal using a second pair of BJTs having emitters coupled to emitters of the first pair of BJTs;
• forming a differential output signal at output nodes defined by cross-coupled collectors of the first and second pairs of BJTs;
• feeding the differential output signal back to the input nodes through a feedback resistor and an emitter follower, wherein the feedback resistor is configured to tune an input impedance of the amplifier;
• regulating a differential bias voltage across the read transducer based on the differential output signal;
• and
• regulating a common-mode voltage at the input nodes based on a voltage sensed at a center tap of a resistive divider connected between the input nodes.