AE Techron LVC2016, Техническое руководство

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Principles of Operation 4-4
4.4 Voltage Amplification
The Voltage Translator stage separates the output of the Error Amp into balanced
positive and negative drive voltages for the Last Voltage Amplifiers (LVAs),
translating the signal from ground referenced ±15V to ±Vcc reference. LVAs
provide the main voltage amplification and drive the High Side output stages.
Gain from Voltage Translator input to amplifier output is a factor of 25.2.
4.4.1 Voltage Translators
A voltage divider network splits the Error Signal (ES) into positive and negative
drive signals for the balanced voltage translator stage. These offset reference
voltages drive the input to the Voltage Translator transistors. A nested NFb loop
from the output of the amplifier mixes with the inverted signal riding on the offset
references. This negative feedback fixes gain at the offset reference points (and
the output of the Error Amp) at a factor of -25.2 with respect to the amplifier
output. The Voltage Translators are arranged in a common base configuration for
non-inverting voltage gain with equal gain. They shift the audio from the ±15V
reference to VCC reference. Their outputs drive their respective LVA.
Also tied into the Voltage Translator inputs are ODEP limiting transistors and
control/protection transistors. The ODEP transistors steal drive as dictated by the
ODEP circuitry (discussed later). The control/protection transistors act as switches
to totally shunt audio to ground during the turn-on delay, or during a DC/LF or
Fault protective action.
4.4.2 Last Voltage Amplifiers (LVAS)
The Voltage Translator stage channels the signal to the Last Voltage Amplifiers
(LVA:s) in a balanced configuration. The +LVA and -LVA, with their push-pull
effect through the Bias Servo, drive the fully complementary output stage. The
LVAs are configured as common emitter amplifiers. This configuration provides
sufficient voltage gain and inverts the audio. The polarity inversion is necessary to
avoid an overall polarity inversion from input jack to output jack, and it allows the
NFb loop to control Error Amp gain by feeding back to its non-inverting input
(with its polarity opposite to the out- put of the VGS). With the added voltage
swing provided by the LVAS, the signal then gains current amplification through
the Darlington emitter-follower output stage.