Analog Devices ADRV9001 User Manual page 67

Preliminary Technical Data
setting the enableFallToOffDelay equal to the time user wish to continue receiving data (Note enableFallToOffDelay is forced to 0
currently by ADRV9001.). This time should be no larger than the guard time before the next frame. The longer this value, the later the
next Rx_enable rising edge can occur. In cases where the receive path has a large propagation delay, user may wish to turn off the
receiver analog front end, so that user may commence a transmit frame, but still leave the digital datapath and interface on so that data
already received over the air may be sent over the interface. The enableHoldDelay parameter is used for this purpose. It must always be
set at least the enableFallToOffDelay. In order to receive all the data already received over the air, it should be set to
enableFallToOffDelay + propagationDelay
Guard/Hold Times Between Edges of TX_ENABLE and RX_ENABLE
By understanding the transmit and receive timing parameters discussed separately in the previous sections, the minimum guard/hold
time design between the rising and falling edges of TX_ENABLE and RX_ENABLE in a TDD system are further discussed in this section.
Six scenarios are considered, as follows:
Guard time between TX_ENABLE falling edge and RX_ENABLE rising edge
•
Guard time between RX_ENABLE falling edge and TX_ENABLE rising edge
•
Guard time between TX_ENABLE falling edge and TX_ENABLE rising edge
•
Guard time between RX_ENABLE falling edge and RX_ENABLE rising edge
•
Hold time between TX_ENABLE rising edge and TX_ENABLE falling edge
•
Hold time between RX_ENABLE rising edge and RX_ENABLE falling edge
•
User should always set the guard/hold timer greater than the minimum requirement. Note no hardware or software restriction prevents
user from raising TX_ENABLE/RX_ENABLE at any time. Correct operation cannot be guaranteed if rules described in the following
sections are violated.
Guard Time Between TX_ENABLE Falling Edge and RX_ENABLE Rising Edge
The guard time between TX_ENABLE falling edge and RX_ENABLE rising edge is for making sure that the transmitter analog front end
and the receiver analog front end are not powered up simultaneously. As discussed in previous sections, after TX_ENABLE falling edge,
it takes t to power off the transmitter analog front end. Therefore, the earliest time the receiver analog front end can be powered
TxEnaFall2Off
up is t after the TX_ENABLE falling edge. Because it takes t
TxEnaFall2Off
RX_ENABLE rising edge, the minimum guard time is t
is less than t (this could be possible when power saving modes are enabled as discussed in later sections), RX_ENABLE rising
RxEnaRise2On
edge could happen t
RxEnaRise2On
Guard Time Between RX_ENABLE Falling Edge and TX_ENABLE Rising Edge
Similarly, the guard time between RX_ENABLE falling edge and TX_ENABLE rising edge is for making sure that the Rx analog front
end and the Tx analog front end are not powered up simultaneously. As discussed in previous sections, after RX_ENABLE falling edge, it
takes t to power off the Rx analog front end. Therefore the earliest time Tx analog front end can be powered up is t
RxEnaFall2Off
the RX_ENABLE falling edge. Because it takes t
rising edge, the minimum guard time is t
t , TX_ENABLE rising edge could happen t
TxEnaRise2On
TxEnaFall2Off
− t before TX_ENABLE falling edge. Figure 57 describes both cases.
TxEnaFall2Off
Tx_ENABLE
t – t
TxEnaFall2Off RxEnaRise2On
Rx_ENABLE
t > t
TxEnaFall2Off RxEnaRise2On
Figure 57. Minimum Guard Time Between TX_ENABLE Falling Edge and RX_ENABLE Rising Edge
to power up the transmitter analog front end starting from the TX_ENABLE
TxEnaRise2On
– t
RxEnaFall2Off TxEnaRise2On
TxEnaRise2On
Rx_ENABLE
t – t
RxEnaFall2Off TxEnaRise2On
Tx_ENABLE
t > t
RxEnaFall2Off TxEnaRise2On
Figure 58. Minimum Guard Time Between RX_ENABLE Falling Edge and TX_ENABLE Rising Edge
to power up the receiver analog front end starting from the
RxEnaRise2On
− t if t
RxEnaRise2On TxEnaFall2Off
Tx_ENABLE
t
RxEnaRise2On
Rx_ENABLE
t
TxEnaFall2Off
if t is greater than t
RxEnaFall2Off
− t before TX_ENABLE falling edge. Figure 58 describes both cases.
RxEnaFall2Off
Rx_ENABLE
t
TxEnaRise2On
Tx_ENABLE
t
RxEnaFall2Off
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is greater than t . In the case of t
RxEnaRise2On
– t
TxEnaFall2Off
< t
RxEnaRise2On
. In the case of t
TxEnaRise2On RxEnaFall2Off
– t
RxEnaFall2Off
< t
TxEnaRise2On
UG-1828
TxEnaFall2Off
after
RxEnaFall2Off
is less than