SAN2202

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1. Data Sheet SA2531/2 Single Chip Telephone

2. Application Note SAN3020: Power extraction for external loads

SAN2202

Application Note (this document)

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

SAN2202a (Shunt path supply)

SAN2202b (Power extraction)

AC impedance

no influence

no influence

off -hook DC mask

no influence

no influence

Tx-/Rx-gains

no influence

no influence

“Make”-resistance in pulse dialing

<230

Ω @ 20mA

<160

Ω @20mA

max. sending level

(soft clip level = 4Vpp)

no influence ; soft clip level

max. 8

Ω output power; THD <2%

≈26mW

≈27mW

max. 8

Ω output power; THD <3%

≈32mW

≈34mW

number of extra components

none

3parts:

1 transistor,1diode,1resistor

3 Other applicable documents and papers

4 Revision status

5 General description