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AD9789 overall gain ?

Question asked by Mathieu on Mar 29, 2012
Latest reply on Apr 6, 2012 by Mathieu

Hi,

I am using an AD9789 in QDUC mode. It is fed with a digital I,Q signal rotating at -500kHz, the AD9789 upconverters it to 474.166MHz. As expected i observe a single CW at the output centered at 473.666 MHz.

The main parameters are :

* AD9789 clock is 2230MHz.

* I and Q digital amplitudes are at maximum, i.e. 0x4000.

* The sumscale and inscale gains are set to 1.0.

* Full scale output current is 20mA.

* Output schematics is the same as Figure 110 on page 56 of AD9789 datasheet rev. A.

 

The output level i expect is 50 Ohms x 20mA volts peak to peak, i.e. +4dBm.

The measurement only shows -10 dBm.

 

Why such a loss ? Is the expected value of +4dBm wrong ? Where are the lost dBms ?

 

Thanks to those who can help

 

Mathieu

 

PS : AD9789 Configuration sequence shown below : Adresse <- Data

 

0x32 0x9E

0x30 0x80

0x24 0x00

0x24 0x80

0x2F 0xCE

0x33 0x42

0x39 0x4E

0x3A 0x6C

0x03 0x00

0x04 0xFE

0x03 0x0C

0x33 0x43

0x06 0xDE

0x08 0x40

0x09 0x20

0x20 0x08

0x21 0x7B

0x22 0x1F

0x23 0xF3

0x25 0x80

0x29 0x00

0x3C 0x00

0x3D 0x02

 

0x05 0x00

0x0A 0x30

0x0B 0x0C

0x0C 0x63

0x1C 0x31

0x1D 0x36

0x1E 0x80

0x24 0x00

0x24 0x80

0x05 0x01

 

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