12/21

MSM6889

¡ Semiconductor

Figure 2

C1 is an ignorable impedance in the voice frequency band; therefore, if a line transformer and

as shown below.

VT, VR

: Transmit at 2W on phone line, receive signal level (balanced)

VT1, VR1

: Transmit at pin 3 (AIN+), receive signal level (unbalanced)

VAO

: Transmit signal level at pin 5 (AO) (unbalanced)

VT2

: Leaking of transmit signal into receive circuit (unbalanced)

VR2

: Receive signal level of the device (unbalanced)

1) VT = VT1 = 1/2 ¥ VAO

The transmit signal level (voltage) on phone line is half the level at the output pin (AO) of the

device. (600 W : a 600 W line transformer is used)

2) VR1 = VR

3)

Then, where R2 = R3 (e.g., 51 kW), VT2 = 0.

This means that the transmit signal is no longer leaking into the receive circuit.

4)

VT VR

600 W : 600 W

C1

2.2 mF

R1

600 W

R2

R3

VT1,VR1

VAO

+

–

+

–

R2,R3 ≥ 20 kW

AO

AIN+

AIN–

GAR

VT2,VR2

3

4

2

5

FUNCTIONAL DESCRIPTION AND APPLICATION

Resistance Hybrid Condition (Ideal Condition)

VT2 = VT1 ¥ (1+

) + VAO ¥ (–

)

R3

R2

R3

R2

=

VAO ¥ (1+

) – VAO ¥

=

VAO ¥ (1–

)

R3

R2

R3

R2

1

2

R3

R2

1

2

VR2 = VR1 ¥ (1+

) , where R2 = R3, VR2 = 2 ¥ VR1 = 2 ¥ VR

R3

R2