3V / 35mW dual power amplifier
Circuit description (refer to the Internal Circuit diagram)
(1) Preamplifier Stage
The preamplifier is comprised of the level-shift transistor
Q101, a differential amplifier (Q102and Q105), and the active
load (Q103and Q106). The input is a PNP transistor that
does not require a coupling capacitor.
(2) Pre-drive stage
Q118is the pre-drive transistor. Q122and Q120form the
(3) Power stage
Comprised of phase-inverting transistor Q120, and power
transistors Q122and Q123.
(4) Idling current setting circuit
The idling current is controlled so that the difference be-
tween the VBEof the power transistor Q122and the VBEof
the phase-inverting transistor Q120is the same as the dif-
ference between the VFof the constant-voltage diode
Q117and the VBEof Q121.
(5) Negative-feedback circuit
The closed-circuit gain with negative feedback is deter-
mined by R108, R102, and the value of the resistor con-
nected to the NFB pin. Part of the gain setting resistance
is on the chip (R102) to reduce variance between compo-
(6) “Pop” noise elimination circuit
The IC has an internal timing circuit (with switch for op-
eration) to reduce the “pop” noise that occurs when pow-
er is applied.
|BA5204F||ROHM||SOP-16||3V / 35mW dual power amplifier|