Tait TB8100 - Power Saving Measures

58 Functional Description TB8100 Installation and Operation Manual
© Tait Electronics Limited June 2005
4.8.1 Power Saving Measures
The following describes the different ways that the modules of a Power Save
base station are able to reduce their power consumption. Service Kit users
select these measures indirectly by selecting values for the Rx cycling time
and the Tx keyup time.
Receiver Signal Path
Cycling
The receiver can be cycled off for a user-definable time, then switched back
on. If a signal is detected, the receiver stays on, otherwise it cycles off again.
There are two levels of cycling: the first involves only the receiver, the
second involves most circuitry in the reciter.
If the Rx cycling time is 100 ms or less, only the PWD_RX power rail is
turned off. This turns off the receiver front end, receiver ADC (Analog to
Digital Converter) and DDC (Digital Down Converter). Once the cycling
time has elapsed, the following occurs:
1. The DSP turns on the PWD_RX power rail.
2. The DSP initialises the DDC. This results in a working receiver.
3. The DSP measures the RSSI to see whether there is a signal on the
channel.
4. If the RSSI does not exceed the threshold, the DSP turns the power
rail off.
The whole process takes about 10ms.
If the Rx cycling time is greater than 100ms, more circuitry (including the
receiver VCO) cycles on and off. In this case, the DSP turns the PWD_RX
and the PWR_ON power rails off (see “Power Distribution” on page 49 for
more information about reciter power rails). Once the cycling time has
elapsed, the following occurs:
1. The DSP turns the PWR_ON rail back on and tells the RISC.
2. The RISC programs the receiver synthesizer and waits for it to lock.
This takes around 20ms.
3. The RISC tells the DSP that the synthesizer is locked.
4. The DSP turns on the PWD_RX power rail back on, and the process
continues as for receiver cycling above.
Transmitt er Keying Normally, the PA uses special Fast Key circuitry to give a fast but controlled
ramp-up of the PA’s power output. In Sleep and Deep Sleep modes (and in
Normal mode, with a Tx keyup time of 5ms or longer), this function is
disabled by turning off the PA 10V power rail (see “Power Distribution” on
page 49 for more information about power rails). This turns off most of the
PA analogue circuitry. The process of keying the transmitter then works like
this: