TB2909FNG,EB

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Linear amplifiers are widely used in audio field due to its ability to amplify a signal without introducing any non-linearity, or distortion, into the signal. In audio field, they are used as both preamp, to boost weak audio signals from the radio, or synthesizer, before further processing and as power amplifiers, to deliver the boosted and processed signal to drive a speaker, for example. Despite its large range of application, there are few distinct types of linear amplifiers, one of them being the Transistor Bias Feedback Network (TB2909FNG), Electrostatic Bias (EB) type.

The TB2909FNG EB amplifier, introduced by Toshiba in 2017, is a type of linear, audio amplifier that improves sound linearity with high efficiency and easy operation. This type of amplifier circuit includes a Positive Emitter-Follower (PEF) circuit and a Voltage Inverting (VI) or Feedback Network circuit. The amplifier provides an increased linearity compared to other types of amplifier due to its combination of a PEF stage with the feedback network.

The PEF stage of the TB2909FNG EB amplifier consists of an NPN transistor biased by a resistive network composed of a series resistor and a stabilized voltage generator. A resistor string connected in series with the base of the transistor is chosen for the transistor bias. To provide the appropriate bias for the transistor, the voltage generator applies a negative voltage to the base of the transistor.

The VI stage of the amplifier is composed of two transistors connected in a feedback network. The first transistor acts as a buffer and is connected to the PEF stage, while the second transistor is connected to the input of the PEF stage. By providing a feedback signal, the second transistor controls the overall gain of the amplifier. This feedback signal is generated by current flowing through the first transistor. The gain of the amplifier can be adjusted by changing the current bias of the first transistor.

The combined circuit of the PEF and VI stages of the TB2909FNG EB amplifier produces a linear output voltage, which is obtained by combining the signal from the PEF stage with the feedback signal from the VI stage. The signal from the PEF stage contains the capacity of the amplifier to amplify signal with minimal distortion, while the feedback signal from the VI stage provides a gain control function. By controlling the bias of the feedback transistor the gain of the amplifier can be adjusted.

Additionally, the TB2909FNG EB amplifier features a sleep mode with extremely low current consumption, making it suitable for portable audio applications. This mode is enabled by reducing the bias current of the amplifier and ensuring the base voltage of the PEF stage is low enough to turn off the amplification circuit. The amplifier can be disabled by simply cutting off the supply current.

In summary, the TB2909FNG EB is an efficient and easy-to-use linear audio amplifier which provides an increased linearity compared to other types of audio amplifier circuits. Its combination of a PEF stage with a VI stage provides additional gain control, while its sleep mode with low current consumption makes it suitable for a wide range of portable audio applications.

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