AMIS-53050 Datasheet, PDF (24/107 Pages) AMI SEMICONDUCTOR – Frequency Agile Transceiver

AMIS-53050 Frequency Agile Transceiver
Data Sheet
5.5 Peak
There are three methods for slicing the received OOK modulated signal to recover the data. The first method is based on setting a
threshold value that is fixed and to which the receiver compares the recovered signal. The other two methods are based on automatic
setting of this threshold level. These automatic threshold methods require an external capacitor on the PEAK pin to operate. Please
refer to the Application Note “Setting up the Data Slicing Modes” for information on proper selection of the capacitor values.
In the averaging method, the transceiver’s low pass filter circuitry is enabled, with a cut-off frequency set below the data rate filter
setting. This filter extracts an average RSSI level as the data slice threshold. The time constant (corner frequency) for this filter is in turn
determined by the value of the capacitor connected to the PEAK pin. 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 should be considered for proper
operation of the external host controller.
In the peak method, the peak detector circuitry is enabled, followed by detection of the maximum input signal level and setting of the
threshold level 6dB lower than the maximum level, respectively. The capacitor connected to the PEAK pin 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.
In the AMIS-53050, the sniff function can be used to adjust the threshold energy level in order to accommodate changes in the external
noise floor and/or the gain of the receiver due to temperature and voltage. This is done by setting a false wake-up value (number of
false wake-ups during a given number of sniff events).
AMI Semiconductor – Jan. 07, M-20639-002
www.amis.com
Figure 12: Peak Capacitance Circuit
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