1.3.2 CARDET

The carrier detect circuit is comparing the RXBPF-output against a constant threshold. The

carrier detect has to go active when the RXIN input-voltage exceeds 5mVp.

V(Line)

V(Vout)

V(RxIn)

V(RXO)

8.9mVrms

31.5mVp

5.0mVp

593mVp

The carrier detect ON-time can be choosen by D8 of the TST-Reg. The OFF-time is defined

by the AGC-stage settling-time of max. 45/(8*Fbaud) plus 12 cycles of Fbaud*64.

Fbaud=600

Fbaud=1200

Fbaud=2400

T (CD-ON) with TST.D8=L

16.7ms

8.33ms

4.17ms

T (CD-ON) with TST.D8=H

8.33ms

4.17ms

2.08ms

T (CD-OFF)

0.3 ... 9.7ms

0.15 ... 4.9ms

0.07 ...2.5ms

1.3.3 MIXER

There are two mixer stages implemented. The analog mixer (default) consists of an unity-gain

amplifier-stage which is switched to inverting or non-inverting mode by the mixer-reference

clock. The digital mixer, enabled with bit TEST_D5=H, consist of a comparator-stage with

hysteresis of appr. 50mV with which the BPF-output gets transferred to digital. This signal

gets combined with the mixer reference clock by an EXOR-gate.

For the two different modulation-depths, different intermediate frequencies are generated by

proper generation of the reference-frequency. (see paragr.: 1.2.1 FREG-GEN)

BD1

Fspace-Fmark

IF

0

600Hz

2700Hz

1

1200Hz

5400Hz

1.3.4 IF-BPF

The mixer-output is fed to the input of the intermediate-frequency filter. According to the two

different IF defined by BD1, this BPF is programmed to these frequencies by the

IF-SC-CLOCK generator.

BD1

Fcenter

Band Width

0

2700Hz

1200Hz

1

5400Hz

2400Hz

The corner-frequencies of the AAF and the SMF are controlled accordingly.

The SC-filter is a 6th order filter with the following characteristics:

Fin / Fcenter

Fc=2.7k

Fc=5.4k

typ. rel. Gain

0.45

1200Hz

2400Hz

-45dB

0.78

2100Hz

4200Hz

-3dB

1.22

3300Hz

6600Hz

-3dB

2.14

5800Hz

11600Hz

-45dB

1.3.5 DEMOD & DATAFIL

The output of the IF-BPF gets transferred to digital by an comparator with pos. AC-feedback

Vhyst~10mV. The periode-time is then measured by a counter which gets set to a proper

starting point, so that at the end of a measurement-periode the frequency-delta is represented

by a 4 bit word. This digital information is transformed again into analog by an DAC which

is included to the input-stage of the SC-Datafilter. No AAF is needed because the DAC is

synchronised with the filter. The unity-gain datafilter can be programmed to three different

corner-frequencies according to the Baudrates of 600,1200 and 2400Hz.

AS5501 / AS5502 Multimode Powerline Modem

Data Sheet

Rev A, May 2000

Page 15/25