YDA137

7

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Description of functions

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Digital Amplifier Function

INL

(INR)

VREFL

(VREFR)

Balanced

Pulse

Width

Modulation

Unit

(L-ch/R-ch)

RI

OUTPL

OUTPR)

LO

LO

CO

CO

RL

Digital Amplifier

Stage

VSSPL1

VPL

(VPR)

YDA137

First Operational

Amplifier Stage

RNP

RNP

VDDPL

VSSPL2

VDDPL

OUTML

OUTMR)

Amplifier function block diagram

Amplifier Section of YDA137 is composed of the first operational amplifier stage and the latter digital amplifier stage.

In digital amplifier stage, digital amplifier output is feed-backed to the modulation circuit, and low distortion rate is

realized.

Digital amplifier output is connected to a speaker through the 2nd-order low-pass filter consisting of inductance (Lo) and

capacitance (Co). This eliminates carrier frequency content existing at the digital amplifier output, consequently only audio

signal is sent to a speaker.

Gain Setting

Gain of the first operational amplifier can be calculated by the following formula. Gain of aｎ internal digital amplifier is

8.0dB.

Gain

First operational amplifier stage

Digital amplifier stage

8.0dB

In this setting value, input sensitivity is 1Vrms, the maximum output could be obtained at 1Vrms input.

Av(dB) = 20×log(39/33) + 8

= 9.5 (dB)

In gain setting of the first operational amplifier stage, it is necessary to obey the restriction that is described in the “Pop

operational amplifier drive capability.