AN4193

Overview of low duty cycle mode

Doc ID 023837 Rev 1

5/10

Finally, the parameter t

RX

can be set based on the following equation:

Equation 2

This will ensure that a node doing RX in LDC mode will be able to receive a packet sent by

a transmitter, which repeats the message for a certain period of time.

Figure 2 shows the minimum RX ON time to ensure a valid sync is captured.

Figure 2.

RX on minimum time for RX timeout on sync

The transmitter needs to repeat the packet to be transmitted for at least t

LDC_cycle

. From this

we can see how the consumption of the receiver is reduced at the expenses of increasing

the consumption on the transmitter side and increasing the latency of response. This may

be perfectly acceptable and desirable, for example, in applications where the receiver is

battery-operated and the transmitter is powered by mains.

1.1.2

RX timeout using RSSI

In this mode, the receiver timeout is stopped upon detection of signal energy above a

certain user defined threshold. This mode will further reduce average power consumption by

decreasing the time when receiver must be on. On the other hand this mode will add some

further burden on the micro which needs to check that a valid message is received within a

user defined timeout.

In this mode, the SPIRIT1 cycles between RX active and sleep as described in

Figure 1; the

only difference is that the minimum time t

RX

will be much smaller than that described in

Section 1.1.1. The time to measure RSSI of the incoming signal will vary according to the

RX filter bandwidth shown in

Table 3.

l

packet

Length of the packet in bits

t

interpacket

Delay between two consecutive transmissions; it is the cumulative time of interrupt

response time, reload of the TX fifo, send TX command, ready to TX transition.

Table 2.

Packet period key parameters (continued)

Name

Description

t

RX

t

p a c k e t _period

l

preamb l e

l

syn c

+

() datarate

⋅

+

≥

AM16917V1