With the bias-current outputs M1M and P1M the transistors T5 and

T6 get switched on and the driver stage is activated. The TxOut1,2 output-currents are in the

range of 3mA with complementary AC-components. For stability-reasons it is needed to

place a capacitor of 150pF from node VX to VSS.

The circuit with T1-T4 is a unity gain buffer structure. The transformer with attached

capacitor Cr gives a resonator for the used frequency-band.

With the shown test-circuit, the harmonic distortion has to be within the following limits with

a power-line load of (5ohms+50uH) // 50ohms:

ratio to the fundamental

2nd Harm.

min. 70dB

3rd Harm.

min. 75dB

higher Harm.

min. 80dB

In receive-mode, when the bias-currents are turned off, the base of the two output-transistors

are forced by resistors of 100k (Rx) to 0V and Vbuf respectively to guarantee high impedance

of the buffer. The current of the pins TxOut1,2 is 0 (VX is floating). Since the receiver-AGC

is reacting on signal levels at the RXBPF-filter output, high outband noise-components could

give clipping in the first stages of the receiver path. To avoid this, aa attenuation of 16dB

with R2, R3, C3 is realized.

(Monochromatic Noise Measurement: Outband-noise with 0dBV @ line w. 80% AM (1kHz)

=> 12.8Vpp after transformer;

=> 2.0Vpp at pin RXIN; )

The resistors R1, R2, R3 are calculated to have a DC-voltages of Vbuf/2 at node Vout and

2.5V at node RXIN. An external diode for protection against high positive voltages is needed

at Vout (Pin TXFB).

AS5501 / AS5502 Multimode Powerline Modem

Data Sheet

Rev A, May 2000

Page 12/25

BC547

BC557

BC557

BC557

2k7

18

1u

0.47u

2.5:1

100

300

150p

2k7

BD140

BD139

BD139

BD140

0V

TXOUT2

TXOUT1

TXFB

P1M

T5

T6

M1M

24V

RXIN

13.3k

10k

3k

330p

24V

24V

0V

0V

R3

R2

R1

C3

C1

Cr

RB

RB

(RB, R1, R2, R3, C3 has to be adjusted

for 12V VBUF version.)

T1

T2

T4

T3

Rx

100k

Rx

100k

24V

Cr has to be adjusted to proper Fcenter.

VX

Vout

Rx

100k

LINE

3k

300

12

6u8

0V

C2

24V

12