Hi.

In the example of "EEsof Knowledge Center>Examples>Application Examples>ADS>2005A>Com_Sys>BlueTooth_prj", using two baseband Gaussian Noise sources(Noise_I, Noise_Q), Noise_RF are created via QAM_MOD.

Here parameters of QAM_MOD are Power=dbmtow(10) and Vref=1.414.

So Noise_RF is created like following.

Noise_RF=A*Real{(Noise_I+j*Noise_Q)*exp(j*wc*t)},

A=sqrt(2*50*dbmtow(10))/1.414=1/sqrt(2)

Then consider average noise power.

<Noise_RF**2>=(A**2)*0.5*{<Noise_I**2>+<Noise_Q**2>}=(A**2)*<Noise_I**2>=(A**2)*<Noise_Q**2>

Here <> means average.

From the above average noise power equatios, I think A should be 1.0 not 1/sqrt(2).

On the other hand we can create Noise_RF using just one Gaussian Noise source with FCarrier=2.4GHz.

Two baseband Gaussian Noise sources with QAM_MOD of A=1.0 can give same result as single Gaussian Noise source with FCarrier=2.4GHz.

How do you think ?

In the example of "EEsof Knowledge Center>Examples>Application Examples>ADS>2005A>Com_Sys>BlueTooth_prj", using two baseband Gaussian Noise sources(Noise_I, Noise_Q), Noise_RF are created via QAM_MOD.

Here parameters of QAM_MOD are Power=dbmtow(10) and Vref=1.414.

So Noise_RF is created like following.

Noise_RF=A*Real{(Noise_I+j*Noise_Q)*exp(j*wc*t)},

A=sqrt(2*50*dbmtow(10))/1.414=1/sqrt(2)

Then consider average noise power.

<Noise_RF**2>=(A**2)*0.5*{<Noise_I**2>+<Noise_Q**2>}=(A**2)*<Noise_I**2>=(A**2)*<Noise_Q**2>

Here <> means average.

From the above average noise power equatios, I think A should be 1.0 not 1/sqrt(2).

On the other hand we can create Noise_RF using just one Gaussian Noise source with FCarrier=2.4GHz.

Two baseband Gaussian Noise sources with QAM_MOD of A=1.0 can give same result as single Gaussian Noise source with FCarrier=2.4GHz.

How do you think ?

To verify this yourself just connect the TkPower component at the output of the QAM_Mod component. Make sure you terminate the output of the QAM_Mod with a matched load (typically 50 Ohms) and set the RefR parameter of TkPower to the same resistance value (TkPower has infinite input resistance; RefR is used only for calculation purposes).

You should see the power reported by TkPower to be 10 dBm. If you change the Power of QAM_Mod to another value the TkPower reading will follow. Please try this yourself and let me know if it does not work. The key in getting the correct power is to properly "calibrate" the QAM_Mod. This is done by setting the VRef parameter of QAM_Mod to the RMS value of the input I/Q signal, that is sqrt( <I+jQ>^2 ) = sqrt( <I^2> + <Q^2> ) since I and Q are uncorrelated. In our case, since VA is the mean of the Gaussian distribution and VB the standard deviation

<I^2> = <Q^2> = VB^2 = 1

and so VRef must be set to sqrt( <I^2> + <Q^2> ) = sqrt( 1 + 1 ) = sqrt(2).

The signal at the output of QAM_Mod is

A*(I+jQ) = ( sqrt( 2*R*P ) / VRef ) * ( I+jQ )

and the mean power is

(sqrt(2*R*P) / VRef)^2 * ( <I+jQ>^2 ) / (2*R) =

( 2*R*P / VRef^2 ) * ( <I^2> + <Q^2> ) / (2*R) =

( 2*R*P / VRef^2 ) * ( VRef^2 ) / (2*R) = P = 10 dBm

On the other hand, the power at the output of the Noise source with FCarrier greater than 0 is:

P = <V^2>/(2*R)

So P = <(I+jQ)^2>/(2*R) = ( <I^2> + <Q^2> )/(2*R) =

(because I and Q are not correlated)

= (1+1)/(2*R) = 1/R = 0.02 (for R = 50)

= 20 mW = 13 dBm.

So it is true that if you set VRef of QAM_Mod to 1 you will get the same result as when using a Noise source with VA=0, VB=1, and FCarrier=1.4GHz but then the noise power will be 13 dBm.

To get a noise power of 10 dBm from a single noise source set VB to 1/sqrt(2).