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AD9963 - voltage on RXCML is 1.75V

Question asked by JackGo on Feb 11, 2013
Latest reply on Feb 12, 2013 by larrywelchusa

Hi,

 

In my circuit RXCML provides common voltage for IQ demodulator. After turning this voltage on using procedure described in datasheet, it becomes 1.37V (RXCML is of course decoupled with 100nF).  After disabling common-mode buffer on ADC inputs by setting bit 1 in 0x7E register (Rx ADC Trim Ctrl) voltage on RXCML rises to about 1.75V. This happens even without demodulator board connected. AD9963 is single supplied with 3.3V. What I'm doing wrong? Should I provide 1.4V for demodulator from another source instead from AD9963?

 

Here is my AD9963 init sequence after resetting it:

[0x31]=0x9F,

[0x3A]=0x55

[0x3B]=0x55,

[0x3C]=0x00

[0x39]=0x00

[0x3E]=0x3F

[0x66]=0x00,

[0x7D]=0x1F,

/* turn on RXCML voltage, Set I/Q offset to 0 */

[0x05]=0x03,

[0x0F]=0x02,

[0x10]=0x00,

[0xff]=0x01,

[0x05]=0x00,

/* disable the common-mode buffer.  */

[0x7E]=0x01

 

Thanks in advance for answer

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