Not understanding the content of DAC3484’s datasheet on page 62

Hello,

The mixing sequence is derived from the equation above Table 8. 

In normal mixer bypassed mode, the mixing frequency Fmix is zero. Thus, the sine terms canceled out, leaving only the cosine terms. This why the mixing sequence is Iout = I1, I2, I3, I4, and Qout is Q1, Q2, Q3, Q4, etc. 

The same principle can apply to fs/2, fs/4, and -fs/4 mixing. Simply substitute t with 0T, 1T, 2T, etc, and fmix with fs/2, fs/4, and -fs/4. You will find out that the sine or cosine terms becomes 1, 0, or -1. This forms the mixing sequence without having to compute the actual mixing using mathematics.

The mixer can be programmed by enabling mixer in config2, bit6, and program the mixer in Config13. See table 9 for detail. 

-KH

Hello,

Here are some examples, and you can apply the same principle to all the mixing sequence:

General Equation:

Iout = In*cost(2*pi*fcmix*t) - Qn*sin(2*pi*fcmix*t)

Qout = In*sin(2*pi*fcmix*t) + Qn*cos(2*pi*fcmix*t)

sample 1, I1, Q1, at 0*T, Fmix = Fs/2

Iout = I1*cos(2*pi*fs/2*0T) - Q1*sin(2*pi*fs/2*0T) = I1

Qout = I1*sin(2*pi*fs/2*0T) + Q1*cos(2*pi*fs/2*0T) = Q1

sample 2, I2, Q2 at 1*T, Fmix = Fs/2

Iout = I2*cos(2*pi*fs/2*1T) - Q1*sin(2*pi*fs/2*1T) = I2*cos(pi) - Q2*sin(pi) = -I2
Qout = I2*sin(2*pi*fs/2*1T) + Q2*cos(2*pi*fs/2*1T) = I2*sin(pi) + Q2*cos(pi) = -Q2

Using the same principle, you may work out the details of the rest of the sequence.

-KH