Analog Devices ADRV9005 Reference Manual page 87

Reference Manual
MICROPROCESSOR AND SYSTEM CONTROL
Table 34. Transmit Timing Parameters Description (Continued)
Transmit Timing Parameters
enableRiseToAnalogOnDelay
(t )
TxEnaRise2AnaOn
enableGuardDelay(t )
TxGT
enableHoldDelay (t )
TxEnaHold
enableFallToOffDelay (t )
TxEnaFall2Off
Design Strategies for Transmit Timing Parameters
Use Case 1: t > t
TXPD TXENASETUP
Here, because the propagation delay is larger than the transmit analog setup delay, delay powering up the AFE while the data is propagating
through the digital datapath, as shown in
delay is 2.5 ms, whereas the enableSetupDelay provided by the ADRV9001 is 8 μs, an AFE can be off to avoid burning power for the first
2.492 ms of the propagation time. Having the analog front end powered up early can also be a liability. For example, if the transmit propagation
path delay is longer than the guard time between receive and transmit frames, the transmit enable rising edge may occur in the middle of a
receive frame. In this case, keep the AFE of the transmitter channel powered down until the end of the receive frame. In such a case, set the
enableRiseToAnalogOnDelay to some value less than or equal to:
propagationDelay – enableSetupDelay.
Set enableRiseToOnDelay equal to the propagationDelay or enableRiseToAnalogOnDelay + enableSetupDelay. The transmit enables rising
edge must occur enableRiseToOnDelay before on air transmit begins. The transmit interface can be set high at the same time as transmit
enables to start transmitting guard symbols.
When the frame ends, the transmit enable falling edge should ideally occur right as the last valid data that must be demodulated by a receiver
sent over the interface. Hold the interface on for some time longer to send guard data across by setting enableHoldDelay to a value greater
than zero. The parameter enableFallToOffDelay determines when the ADRV9001 transmit AFE is powered down after the transmit enables
falling edge, and the antenna is switched away from the transmit channel if the antenna switch is enabled. Always set it to a value greater than
or equal to enableHoldDelay. If both values are set equal, for example, both are set to 0, the interface turns off first, then analog powers down.
To ensure all the data sent over the interface makes it onto the air, set enableFallToOffDelay greater than or equal to:
enableHoldDelay + propagationDelay.
If it is greater, then zeros are transmitted after all the data sent over the interface is propagated.
Use Case 2: t < t
TxPD TxEnaSetup
In this case, as shown in Figure
than the time to set up the AFE t
after the TX_ENABLE rising edge. The parameter enableRiseToOnDelay can also be set to 0. Here, the antenna is switched to a transmit
channel, as soon as analog power up completes. For a more deterministic delay between the transmit enable rising edge and antenna switch
time, set enableRiseToOnDelay to a value greater than or equal to:
analog.com
Provided by Bounds
User parameter Min: 0
Max: t
TxEnaRise2On
User parameter Min: N/A
Max: N/A
User parameter Min: 0
Max: None. Must be optimized
to be minimal.
User parameter Min: t
TxEnaHold
Max: None. Must be optimized
to be minimal.
(Recommended Max: t
+ t Note t
TxPD TxEnaHold
to 0 currently.)
Figure 68. This saves power by reducing unnecessary AFE on time. For example, if the propagation
69, the time taken for data to propagate from the digital interface to antenna is very small, i.e. , t
. In such a case, set enableRiseToAnalogOnDelay to 0, so that analog power up begins immediately
TxEnaSetup
Comments
At typical value: all symbols sent over the interface (including guard symbols)
make it onto the air.
At maximum bound: no guard symbols are transmitted over the air.
If the transmit propagation delay is long, delay the analog power up for power
saving or to keep transmit analog powered down during receive frame. If the
− t
TxEnaSetup
transmit propagation delay is small, set this to 0. If this parameter is greater than
its maximum bound, delay the antenna switch time.
Reserved, not used.
Tx_enable falling edge must ideally come as the last valid data is sent over the
interface. Use this to disable the transmit algorithms, whose performance may be
degraded if guard symbols are used. Keep the interface on even after Tx_enable
falling edge to allow the transmission of user guard symbols.
At minimum bound: antenna switch occurs soon after the transmit interface is
disabled. It should always occur before powering down of the transmit analog.
Not all symbols in the path make it on air.
At maximum bound: antenna is switched away from the transmit channel just as
TxEnaHold
is forced the last user data has propagated to the antenna.
ADRV9001
is smaller
TxPD
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