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Hi,
Many thanks for previous previous replies!
I am aware that there is a program that calibrates the DC offset and writes the DC values to the EEPROM and I have used it (requires a serial connection to my WARP v2 baord, etc) . My question is simple, if you do not use the automatic gain control (AGC), will the DC offset be present in the signal?
It's just that I notice that AGC seems to control DC offset as well as gain. I would prefer to control my Rx gain and not use AGC but I don't want DC offset, particularly at the Tx side.
Best Regards,
Pat
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The Tx DCO calibration values are written to the EEPROM during manufacturing. These values are read and applied during the boot process of the various reference designs. These only affect the DC offset applied inside the Tx DACs. The Tx DCO values do not affect the Rx path.
The AGC cores estimate and correct Rx DCO. They do not affect Tx DCO. The Rx baseband signal in the MAX2829 has large DC transients following gain changes. The RXHP pin is asserted during gain changes to reduce the transients observed by the ADC, but a residual DC level persists even after the RXHP pin is de-asserted. There is also a very slow decay in the DC level in the Rx baseband signal following de-assertion of RXHP. The AGC cores handle both issues. Immediately following de-assertion of RXHP the cores estimate the DC level in the I and Q signals (this requires the signal have a preamble with a zero-mean periodic structure) and digitally subtracts this offset. Following this estimation/subtraction the cores implements an IIR high-pass filter with very low cutoff frequency. This filter minimizes the "DC" variations during the reception (it's not technically DC if it's varying, but it's so slow that it's easier to think of it as decaying DC offset). Both of these systems are reset when the AGC is reset at the end of a reception.
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