Analog Devices ADRV9002

Preliminary Technical Data UG-1828
Rev. PrB | Page 67 of 277
ends, but 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, users may wish to turn off the
receiver analog front end, so that users 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
The 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
TxEnaFall2Off
to power off the transmitter analog front end. Therefore, the earliest time the receiver analog front end can be powered
up is t
TxEnaFall2Off
after the TX_ENABLE falling edge. Because it takes t
RxEnaRise2On
to power up the receiver analog front end starting from the
RX_ENABLE rising edge, the minimum guard time is t
TxEnaFall2Off
− t
RxEnaRise2On
if t
TxEnaFall2Off
is greater than t
RxEnaRise2On
. In the case of t
TxEnaFall2Off
is less than t
RxEnaRise2On
(this could be possible when power saving modes are enabled as discussed in later sections), RX_ENABLE rising
edge could happen t
RxEnaRise2On
− t
TxEnaFall2Off
before TX_ENABLE falling edge. Figure 57 describes both cases.
Tx_ENABLE
Rx_ENABLE
t
TxEnaFall2Off
– t
RxEnaRise2On
Tx_ENABLE
Rx_ENABLE
t
RxEnaRise2On
– t
TxEnaFall2Off
t
TxEnaFall2Off
> t
RxEnaRise2On
t
TxEnaFall2Off
< t
RxEnaRise2On
24159-058
Figure 57. Minimum Guard Time Between TX_ENABLE Falling Edge and RX_ENABLE Rising Edge
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
RxEnaFall2Off
to power off the Rx analog front end. Therefore, the earliest time Tx analog front end can be powered up is t
RxEnaFall2Off
after
the RX_ENABLE falling edge. Because it takes t
TxEnaRise2On
to power up the transmitter analog front end starting from the TX_ENABLE
rising edge, the minimum guard time is t
RxEnaFall2Off
– t
TxEnaRise2On
if t
RxEnaFall2Off
is greater than t
TxEnaRise2On
. In the case of t
RxEnaFall2Off
is less than
t
TxEnaRise2On
, TX_ENABLE rising edge could happen t
TxEnaRise2On
− t
RxEnaFall2Off
before TX_ENABLE falling edge. Figure 58 describes both cases.
Rx_ENABLE
Tx_ENABLE
t
RxEnaFall2Off
– t
TxEnaRise2On
Rx_ENABLE
Tx_ENABLE
t
TxEnaRise2On
– t
RxEnaFall2Off
t
RxEnaFall2Off
> t
TxEnaRise2On
t
RxEnaFall2Off
< t
TxEnaRise2On
24159-059
Figure 58. Minimum Guard Time Between RX_ENABLE Falling Edge and TX_ENABLE Rising Edge