
TA2131FNG
2006-04-19
6
Function Explanation
1.
Bass Boost Function
1-1
Description of Operation
TA2131FNG has a bass boost function for bass sound reproduction built-in to the power amplifier.
With the bass boost function, at medium levels and lower, channel A and channel B are added for the
low frequency component, and output to BST amplifier 2 (BST2) in negative phase. That signal is
inverted and added before being subjected to bass boost. If the signal of the low-frequency component
reaches a high level, the boost gain is controlled to main a low distortion (see Fig.1).
1-2
AGC Circuit
The AGC circuit of the bass boost function detects with “AGC DET” the voltage component created
by “BST2,” and as the input level increases, the variable impedance circuit is changed, and the bass
boost signal is controlled so that it is not assigned to BST amplifier 1. In this way, the bass signal to
“BST2” input is shut-off, and that boost gain is controlled.
1-3
Bass Boost System
As shown in Fig.1, the flow of the bass boost signal is that the signal received from power amplifier
input goes through LPF1, ADD amplifier, ATT (variable impedance circuit), BPF1 (BST amplifier 1)
and LPF2, and the negative phase signal to the power amplifier input signal is output from BST
amplifier 2. The reason why it becomes the negative phase of the BST amplifier 2 signal is that the
phase is inverted by 180° in the audible bandwidth by the secondary characteristics of LPF1 and
LPF2 in Fig.1.
Ultimately the main signal and the bass boost signal formed before BST2 are added.
Fig.2 shows the frequency characteristics to each terminal.
Figure 1
System Diagram of Bass Boost
V (RL)
DAC
OUT
20
k
22
21
2
Vref
AGC
IN
ADD
LPF2
BST OUT
BST NF1
Vref
INA
BST
AGC
BST2
PWA
PWB
5
6
BST1
11
10
9
8
7
4
RL
INB
LPF1
DET
OUTB
BST
NF2
OUTA
20
k
20
k
10
k
10
k
10
k
10 k
10 k
15 k
10 k
15 k
10 k
10 k
20 k
2
k
20 k
10 k
12 k
5 k
20 k
30 k
16
220
F
1
F
220
F
22
k
0.
1
F
0.
1
F
Vref
0.
1
F
0.
1
F
4.
7
F
V (LPF1)
V (NF1)
V (LPF2)
V (BST OUT)
V (NF2)
V (OUT)
RL
16
10
F
10
F