
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