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TA2123AF

TOSHIBA Bipolar Integrated Circuit Silicon Monolithic

Toshiba 

TA2123AF

Application Note

1. Preamplifier stage

(1) Output DC voltage of preamplifier

Output DC voltage of preamplifier is determined

by external resistors R1 and R2 as shown in Fig.1.

⊿V

=

28.6mV

R1

+

−R2

VREF OUT

VO (PRE) = VREF OUT-∆V × (R2 / R1 + 1)

Fig.1 Output DC voltage of preamplifier

· VREF OUT = 0.73V (typ.)

· ∆V is an offset voltage which is designed to 28.6mV.

It is as follows in case that the DC voltage is calculated by the constant of a test circuit.

VO (PRE) = 0.73V-28.6mV (200kΩ / 22kΩ + 1)

=0.44V

Output DC voltage of preamplifier should be fixed about VCC / 2, because preamplifier get a enough

dynamic range.

(2) AMS (automatic music sensor) function

A block diagram is shown in Fig.2. This function can AMS (automatic music sensor) and BS (blank skip).

· The comparator input level is higher than comparator sensitivity.

→Rectangle wave is outputted.

· The comparator input level is lower than comparator sensitivity.

→High level is outputted.

The sensitivity changeover is determined by AMS switch (the comparator sensitivity doesn’t change.).

· Automatic music sensor mode

The AMS SW is also turned on when the MT SW is turned on. And the comparator input level is

determined by external resistors (R4~R6) and capacitors (C3, C4) from mixer amplifier output

level.

The transfer function is as follows.

VO / Vi = R3 / [R1･R2 / (R1 + R2)] × {jωC4･R5･R6 / [R4･R5 + jω (C3･R4･R5 + C4･R4･R5 +

C4･R4･R6 + C4･R5･R6) - ω2C3･C4･R4･R5･R6]}

7

2002-10-30

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