MC33596_10 Datasheet, PDF (22/70 Pages) Freescale Semiconductor, Inc – PLL Tuned UHF Receiver for Data Transfer Applications

Receive Mode
Each time is defined with the associated value found in the RXONOFF register.
• On time = RON[3:0] × 512 × T_digclk (see Table 16; begins after the crystal oscillator has started)
• Off time = receiver off time = N × T_Strobe + MIN (T_Strobe / 2, receiver on time), with N decoded
from ROFF[2:0] (see Table 17)
The strobe oscillator is a relaxation oscillator in which an external capacitor C13 is charged by an internal
current source (see Figure 46). When the threshold is reached, C13 is discharged and the cycle restarts.
The strobe frequency is F_Strobe = 1/T_Strobe with T_Strobe = 10⁶ × C13.
In receive mode, setting the STROBE pin to V_CCIO at any time forces the circuit on. As V_CCIO is above
the oscillator threshold voltage, the condition on which the STROBE pin is set to V_CCIO is detected
internally, and the oscillator pulldown circuitry is disabled. This limits the current consumption. After the
STROBE pin is forced to high level, the external driver should pass via a “0” state to discharge the
capacitor before going to high impedance state (otherwise, the on time would last a long time after the
driver release).
When the strobe oscillator is running (i.e., during an off time), forcing the STROBE pin to V_GND stops the
strobe clock, and therefore keeps the circuit off.
Figure 14 shows the associated timings.
Threshold
STROBE
STROBE
Clock
Off
Counter
Digital
Clock
On
Counter
Receiver
Status
0
RON
t_Strobe
0
ROFF-1ROFF
0
Off
Cycling Period
0
RON
On
Off
STROBE
SET TO V_CCIO
RON
On
Crystal Oscillator Startup
Figure 14. Receiver On/Off Sequence
11.4 Received Signal Strength Indicator (RSSI)
11.4.1 Module Description
In receive mode, a received signal strength indicator can be activated by setting bit RSSIE.
The input signal is measured at two different points in the receiver chain by two different means, as
follows.
• At the IF filter output, a progressive compression logarithmic amplifier measures the input signal,
ranging from the sensitivity level up to –50 dBm.
MC33596 Data Sheet, Rev. 4
22
Freescale Semiconductor