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UBA2050

One-chip telephone ICs with speech, dialler and ringer functions

Philips Electronics 

Philips Semiconductors

One-chip telephone ICs with speech,

dialler and ringer functions

Product specification

UBA2050(A); UBA2051(A;C)

Earpiece amplifier (pins GAR and QR)

The earpiece amplifier is an operational amplifier having

its output QR and inverting input GAR available. It can be

used in conjunction with two resistors to get some extra

gain or attenuation.

Arrangements of the receive and earpiece amplifier are

illustrated in Fig.13. Earpiece connections are shown

in Fig.14.

In the basic configuration (see Fig.13), output RX drives

the earpiece amplifier by means of RE1 connected

between pins RX and the inverting input GAR. Feedback

resistor RGAR of the earpiece amplifier is connected

between pins QR and GAR. Output QR drives the

earpiece via a series capacitor Cear.

The gain of the earpiece amplifier (from RX to QR) can be

set between +12 and −14 dB by means of resistor RGAR.

The preferred value of RE1 is 100 kΩ.

The earpiece amplifier offers a gain boost facility relative

to the initial gain. Resistor RGAR has to be replaced by the

network of RGAR1, RGAR2 and Rgb and a series capacitor

Cgb as shown in Fig.13.

The initial gain is defined by: -VV----QR---XR-- = –R-----G----A---R---1-R---+-E---1-R----G----A---R---2-

which corresponds to Rgb = ∞.

The gain boost is realised by a defined value of Rgb and is

defined by:

V-V----QR---XR--

=

–





R-----G----A---R---1-R---+-E---1-R----G----A---R---2-

×









1

+

--RR--------GG--------AA------RR--------11--R------+×---g-----b--RR--------G-G-------AA--------RR------22--





External capacitors CGAR (connected between pins

QR and GAR) and CGARS (connected between pins GAR

and GND) ensure stability. The capacitor CGAR provides a

first-order low-pass filter. The cut-off frequency

corresponds to the time constant CGAR × RGAR. The value

of CGARS must be 10 times the value of CGAR to ensure

stability.

The output voltages of the earpiece amplifier and the

DTMF amplifier are specified for continuous wave drive.

The maximum output voltage swing depends on the

DC line voltage VLN, the DC resistance RCC of the

set-impedance network between pins LN and VCC, the

current consumption ICC and IP from pin VCC and the load

impedance at pin QR.

handbook, full pagewidth

Cear

Rexch

Vexch

Iline Rline

RCC

ICC

RGAR

CGAR

RE1

LN

VCC QR

GAR RX

EARPIECE

AMPLIFIER

0.5VCC

CGARS

earpiece

CVCC

100 µF

Rgb

Cgb

RGAR2

RGAR1

CGARS

RE1

UBA205xx

GND

CGAR

QR

GAR

RX

Addition for gain boost of earpiece amplifier

FCA133

Fig.13 Receive and earpiece amplifier configuration.

2000 May 19

13

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