G1421 datasheet(21/24 Pages) GMT

21 / 24 page

Ver: 1.6

Aug 04, 2005

TEL: 886-3-5788833

http://www.gmt.com.tw

G1421

Global Mixed-mode Technology Inc.

Application Information

Input MUX Operation

There are two input signal paths – HP & Line. With the

prompt setting, G1421 allows the setting of different

gains for BTL and SE modes. Generally, speakers

typically require approximately a factor of 10 more

gain for similar volume listening levels as compared

with headphones.

SE Gain(HP) = -(RF(HP)/RI(HP))

BTL Gain(LINE) = -2(RF(LINE)/RI(LINE))

To achieve headphones and speakers listening parity,

(RF(LINE/RI(LINE)) is suggested to be 5 times of (RF(HP)/

RI(HP)). The ratio of (RF(HP)/RI(HP)) can be determined by

the applications. When the optimum distortion per-

formance into the headphones (clear sound) is impor-

tant, gain of –1 ((RF(HP) / RI(HP)) = 1) is suggested.

Single Ended Mode Operation

G1421 can drive clean, low distortion SE output power

into headphone loads (generally 16

Ω or 32Ω) as in

Figure A. Please refer to Electrical Characteristics to

see the performances. A coupling capacitor is needed

to block the dc offset voltage, allowing pure ac signals

into headphone loads. Choosing the coupling capaci-

tor will also determine the 3 dB point of the high-pass

filter network, as Figure B.

fC=1/(2πRLCC)

For example, a 68uF capacitor with 32

Ω headphone

load would attenuate low frequency performance be-

low 73Hz. So the coupling capacitor should be well

chosen to achieve the excellent bass performance

when in SE mode operation.

Bridged-Tied Load Mode Operation

G1421 has two linear amplifiers to drive both ends of

the speaker load in Bridged-Tied Load (BTL) mode

operation. Figure C shows the BTL configuration. The

differential driving to the speaker load means that

when one side is slewing up, the other side is slewing

down, and vice versa. This configuration in effect will

double the voltage swing on the load as compared to a

ground reference load. In BTL mode, the peak-to-peak

voltage VO(PP) on the load will be two times than a

ground reference configuration. The voltage on the

load is doubled, this will also yield 4 times output

power on the load at the same power supply rail and

loading. Another benefit of using differential driving

configuration is that BTL operation cancels the dc off-

sets, which eliminates the dc coupling capacitor that is

needed to cancelled dc offsets in the ground reference

configuration. Low-frequency performance is then lim-

ited only by the input network and speaker responses.

Cost and PCB space can be minimized by eliminating

the dc coupling capacitors.

VDD

Vo(PP)

Figure A

VDD

Vo(PP)

Figure A

-3 dB

Figure B

-3 dB

Figure B

VDD

Vo(PP)

VDD

-Vo(PP)

2xVo(PP)

Figure C

VDD

Vo(PP)

VDD

-Vo(PP)

2xVo(PP)

Figure C

G1421 Datasheet(PDF) 21 Page - Global Mixed-mode Technology Inc

G1421 Datasheet(HTML) 21 Page - Global Mixed-mode Technology Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL