AMIS-53000 Datasheet, PDF (22/99 Pages) AMI SEMICONDUCTOR – Frequency Agile Transceiver

AMIS-53000 Frequency Agile Transceiver
Data Sheet
5.5 Peak
The AMIS-53000 has three modes for slicing the received signal to recover the data. One method is to set a threshold value that is
fixed and to which the receiver compares the recovered signal. The other two methods have the AMIS-53000 automatically setting a
threshold level to which the receiver compares the recovered signal. Both of these automatic threshold methods require an external
capacitor on the PEAK pin to operate.
In the averaging method, the AMIS-53000 simply adds a low pass filter with a cutoff frequency set below the data rate filter setting.
This second filter extracts an average RSSI level as the data slice threshold. The capacitor on the PEAK pin sets the time constant
(corner frequency) for this filter. A typical capacitor value would allow the average level to settle to 95 percent of the RSSI level in 2 bit
intervals (remember that Manchester encoding may have transitions twice the data rate). The average threshold method will have
chatter before a signal is received and after the signal ends which the external host/controller must be able to handle.
In the peak method the AMIS-53000 uses a peak detector to find the maximum input signal level and then sets the threshold 6dB lower
than that level. The external peak capacitor is used to bleed or discharge the peak voltage in the circuit. The voltage swing on the
RSSI for a typical 12dB signal to noise ratio at 10^-3 BER is 240mV. The capacitor value should not change the voltage by more than
this 240mV during a string of zeros. The value is dependent on the number of zeros that are allowed in the chosen data protocol, NRZ
or Manchester encoded.
Figure 12: Peak Capacitance Circuit
AMI Semiconductor – Aug. 05, Rev. 1.0
22
www.amis.com