Analog Devices ADRV9005 Reference Manual page 90

Reference Manual
MICROPROCESSOR AND SYSTEM CONTROL
Once timing on air is established, raise RX_ENABLE some time before the start of the actual frame. As soon as the receiver analog power up
completes, the digital interface turns on. However, if the path has a long propagation delay, the initial data coming off the interface is not the
data received over the air.
When the frame ends, the users wish to continue receiving for a while. However, the ADRV9001 wishes to stop all the tracking algorithms
to avoid any performance degradation. Achieve this by bringing the RX_ENABLE signal low as soon as the frame ends, but setting the
enableFallToOffDelay equal to the time the user wishes to continue receiving data (Note that enableFallToOffDelay is forced to 0 currently
by the ADRV9001.). This time should not be larger than the guard time before the next frame. The longer this value is, a delay in the next
Rx_enable rising edge can occur. In cases where the receive path has a large propagation delay, turn off the receiver AFE to start 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. Use the
enableHoldDelay parameter for this. Always set it at least to the enableFallToOffDelay. To receive all the data already received over the air, set
it to:
enableFallToOffDelay + propagationDelay.
Guard/Hold Times Between Edges of TX_ENABLE and RX_ENABLE
Based upon the understanding of the transmit and receive timing parameters discussed separately in the previous sections, this section further
discusses the minimum guard/hold time design between the rising and falling edges of TX_ENABLE and RX_ENABLE in a TDD system. There
are six scenarios:
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
►
Always set the guard/hold timer greater than the minimum requirement. Note that no hardware or software restriction prevents from raising
TX_ENABLE/RX_ENABLE at any time. The correct operation cannot be guaranteed if the 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 makes sure the transmitter and the receiver AFE are
not powered up simultaneously. As discussed in the previous sections, after TX_ENABLE falling edge, it takes t
the transmitter AFE. Therefore, the earliest time the receiver AFE can be powered up is t
Because it takes t
RxEnaRise2On
− t if t is greater than t
RxEnaRise2On TxEnaFall2Off
saving modes are enabled as discussed in the following sections), RX_ENABLE rising edge can happen t
TX_ENABLE falling edge. Figure 71
Figure 71. 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 makes sure the receiver and the transmitter AFE
are not powered up simultaneously. As discussed in the previous sections, after RX_ENABLE falling edge, it takes t
the receiver AFE. Therefore, the earliest time transmitter AFE can be powered up is t
it takes t to power up the transmitter AFE starting from the TX_ENABLE rising edge, the minimum guard time is t
TxEnaRise2On
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to power up the receiver AFE starting from the RX_ENABLE rising edge, the minimum guard time is t
. For t
RxEnaRise2On
describes both cases.
TxEnaFall2Off
is less than t
TxEnaFall2Off RxEnaRise2On
RxEnaFall2Off
ADRV9001
to power off
TxEnaFall2Off
after the TX_ENABLE falling edge.
(this can be possible when power
− t
RxEnaRise2On TxEnaFall2Off
RxEnaFall2Off
after the RX_ENABLE falling edge. Because
RxEnaFall2Off
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TxEnaFall2Off
before
to power off