UDA1380 datasheet(13/68 Pages) ICST

13 / 68 page

2002 Sep 16

Philips Semiconductors

Product speciﬁcation

Stereo audio coder-decoder

for MD, CD and MP3

UDA1380

8.2

ADC analog front-end

The analog front-end of the UDA1380 consists of one

stereo ADC with a selector in front of it (see Fig.6). Using

this selector one can either select the microphone input

with the microphone amplifier (LNA) with a fixed 29 dB

gain and VGA (no PGA, since a real microphone amplifier

is much better with respect to noise), or the line input which

has a PGA for having 0 or 6 dB gain (for supporting 1 and

2 V (RMS) input). The PGA also provides gain control from

0 to 24 dB in steps of 3 dB.

Remarks:

• The input impedance of the PGA (line input) is 12 kΩ, for

the LNA this is 5 k

Ω

• The LNA is standard equipped with a microphone power

supply. Since this normally requires two extra pins, this

feature will not be used inside the UDA1380. Instead,

the microphone supply block is replaced by the VGA

block.

8.2.1

APPLICATIONS AND POWER-DOWN MODES

The following Power-down modes and functional modes

are supported:

• Power-down mode in which the power consumption is

very low (only leakage currents)

In this mode there is no reference voltage at the line

input

• Line input mode, in which the PGA can be used

• Microphone mode, in which the rest of the non-used

PGAs and ADCs are powered-down

• Mixed PGA and LNA mode: one line input and one

microphone input.

More information on the analog frond-end is given in

Section 8.11.1.

handbook, full pagewidth

PGA

ADC

SEL_MIC

bitstream

right

ADC

SDC

bitstream

left

MGU530

PGA

(27)

(29)

(31)

VINL

VINR

VINM

SDC

LNA

SDC

Fig.6 Analog front-end.

Pin numbers for UDA1380HN in parentheses.

8.2.2

LNA WITH VGA

The LNA is equipped with a VGA. The function of the VGA

is to have additional variable analog gain from 0 to 30 dB

in steps of 2 dB. This provides more flexibility in the choice

of the microphone.

8.2.3

APPLICATIONS WITH 2V(RMS) INPUT

For the line input it is preferable to have 0 dB and 6 dB

gain settings in order to be able to apply both

1 and 2 V (RMS) input signals, using a series resistance.

For this purpose a PGA is used which has 0 to 24 dB gain,

in steps of 3 dB.

UDA1380 Datasheet(PDF) 13 Page - Integrated Circuit Systems

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