The received signal gets filtered by the BANDPASS filter. An AGC-function is implemented

in this filter, to have improved performance over a wide range of input signal amplitude. The

filtered signal gets transferred to a low frequency band by the use of an MIXER-CIRCUIT so

that the frequency-band can be further reduced by an additional IF_BANDPASS. The

IF-filter output-signal gets DEMODULATED, FILTERED and SYNCHRONIZED to a

receive-clock. In receive mode the CLOCK-RECOVERY circuit is generating the

receive-clock locked to the RX-data edges. The input signal gets compared with a fixed

CARRIER DETECT threshold to get valid RX-data to be further processed by the connected

CPU only.

1.3.1 RXBPF

The bandpass-filter eliminates the frequency components which are not of interest. The

Bandwidth is programmable in 3 steps with the control-bits RXBW1 and RXBW2.

RXBW1 RXBW2 BW/Fcenter BW @ 72.00kHz BW @ 82.05kHz BW @ 132.45kHz

0

0

+/-4.2%

6.0kHz

(6.8kHz)

(11.0kHz)

1

0

+/-1.8%

(2.6kHz)

3.0kHz

4.8kHz

0

1

+/-2.3%

(3.3kHz)

(3.7kHz)

(6.0kHz)

The center-frequency of the filter is defined by the SC-Clock-Frequency (MRK-REG and the

bits BD1,2) in steps of 150Hz. (See paragraph 1.2.1 FREG_GEN).

Frequency-Response with RXBW1=1, RXBW2=0:

Fin / Fcenter

typ. rel. Gain

0.67

-45dB

0.98

-3dB

0.99

0.0dB

1

reference

1.01

0.0db

1.02

-3dB

1.5

-45dB

As already mentioned in the transmitter description, the AAF and SMF of the bandpass-filter

are tuned according to the SC-Clock and therefore to the BPF-centerfrequency.

An additional attenuation of the mains-frequency (50Hz ..) is not needed because of the

external coupling which is already a very good filter for that.

The input-voltage range which has to be handled is 1.5mV ... 1.5Vrms. The signal of the

input-pin RXIN gets buffered and lowpass-filtered by the RXBUF with a fixed gain of 0.66.

(Max. input level 14Vpp@transformer =>2.2Vpp@Rxin =>1.5Vpp@FilterInput)

The gain of the SC-BPF is controlled by the AGC loop to keep the filter-output RXO

constant at 1.0Vp for a wide range of input-dynamic. In total there is a variable gain from -3.6

to +41.4dB in steps of 1dB.

V(Line)

V(Vout)

V(RxIn)

V(RXO)

min -56.5dBV = 1.5mVrms 3.75mVrms = 10.6mVpp

1.7mVpp

0.20Vpp

max

+6dBV = 2.0Vrms

5.0Vrms = 14.0Vpp

2.2Vpp

1.45Vpp

The window-comparator threshold for the AGC-control is set to 1.02V+/-12%. The

AGC-UDC will be clocked by 8*Fbaud which gives a max. settling time of 9.4ms at 600bps.

AS5501 / AS5502 Multimode Powerline Modem

Data Sheet

Rev A, May 2000

Page 14/25