SAN2202 Просмотр технического описания (PDF) - South African Micro Electronic Systems

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SAN2202

SINGLE CHIP “SPEAKERPHONE” WITH 8 - OHM LOUDSPEAKER AMPLIFIER

South African Micro Electronic Systems 

SAN2202

3 Other applicable documents and papers

1. Data Sheet SA2531/2 Single Chip Telephone

2. Application Note SAN3020: Power extraction for external loads

4 Revision status

SAN2202

Application Note (this document)

5 General description

The amplifier is a simple, low cost add-on circuit to the SA253x single chip telephone family. It is supplied by the

line current and amplifies the receive signal, taken from either RO1 or RO2 (Receive outputs), see Fig.1.

Compared to more complex “real” handsfree circuits there is no channel switching or anti-larsen circuit

implemented, therefore the receive and transmit gains must be lower to avoid howling.

However, at short distances between user and telephone (<2m, which is adequate for normal office work) there is

even full duplex “handsfree” operation possible, when the handset is placed next to the telephone with the

microphone facing to the user.

Due to the excellent sidetone cancellation of the SA253x circuits, howling between handset microphone and

loudspeaker will only occur, when both are put very close to each other. In normal operation, no howling will occur,

even with maximum loudspeaker volume.

Due to the unique structure of the SA253x family’s line adaption, adding the amplifier has no influence on the

important PTT related parameters, like AC-impedance, DC-mask, etc. (see Pt. 5.1 below).

Note: all subsequent component numbering refers to the schematic, shown in Pt. 9

5.1 Amplifier supply: Comparison of SAN2202a and SAN2202b:

The following table describes the difference between the two types of amplifier supply: while the simple SAN2202a

supply shows slight influence in maximum sending level and “Make”-resistance in pulse dialing , the SAN2202b (3

extra components) supply has no influence in these parameters and has a more stable maximum output driving

capability at high line currents (see Fig.4 & 5).

Parameter

AC impedance

off -hook DC mask

Tx-/Rx-gains

“Make”-resistance in pulse dialing

max. sending level

(soft clip level = 4Vpp)

max. 8Ω output power; THD <2%

max. 8Ω output power; THD <3%

number of extra components

SAN2202a (Shunt path supply)

no influence

no influence

no influence

<230Ω @ 20mA

no influence for ILine <40mA

<4Vpp for ILine >40mA (see.Fig.3)

≈26mW

≈32mW

none

SAN2202b (Power extraction)

no influence

no influence

no influence

<160Ω @20mA

no influence ; soft clip level

≈27mW

≈34mW

3parts:

1 transistor,1diode,1resistor

3/9

sames

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