QI have some questions regarding “Image Rejection Calibration” procedure for the
ADF7021-N, indicated in following Preliminary Apps Note:
“Put the ADF7021 into receive mode. The AGC should be set to Manual mode. The
LNA gain should be set to minimum level in register 9 by setting LNA gain =
0x0, LNA current = 0x3 and Filter gain = 0x1”
1)Does it mean i go through the entire power-up sequence for receive mode then
set register 9.
2)It also says “LNA current = 0x3”, what is this referring to. I can find no
such register entry.
3)Do you really mean set filter gain to 0x1 i.e. 24 or do i use the min level
0x0 i.e. 8.
4)I have used the application note to write code to adjust the I channel phase
and gain to get lowest RSSI, can i please just confirm that i can leave the Q
channel as is.
A1) Yes, refer to Figure 26 in the datasheet for further details.
2)This is the LNA_BIAS bits (bits 26,27).Refer to AD7021 datasheet. I am
waiting to confirm the current value when these bits are set to 0x3.
3)Filter gain should be set 0x1 as described. With these settings, the internal
source will be strong enough to be read accurately by the RSSI circuitry. In
fact, if the results are not returning the optimum IR cal settings, you could
try experimenting with slightly higher filter and LNA gains. In particular, if
using external source these settings may not be optimum.
4)Yes you can leave the Q-channel as is.