Design of Double down conversion of superhyterodyne receiver

[sanketachari]

Hello,

I am designing 'Double down conversion of superhyterodyne receiver' for the frequency range of 54MHz - 860 MHz . I am using the following design. Here I have given 700 MHz as RF input.



Design parameters set are unable to generate the frequency response & respective voltage output, noise figure, S parameters graphs. Can anybody help me design the above model & guide about required parameters to be set ?

Thanks.

 

[chuckey]

I do not understand why you have a first IF of 400 MHZ, this will leave a "hole" in your frequency coverage around that frequency. I have not heard of a receiver that will receive its own IF frequency.
Your second IF, is unusual, TV sets use 38.9 MHZ ( lots of standard components available), or if your are really worried about spurious signals, 22.5 MHZ.
Every stage before the main IF filter has to be extremely linear or cross modulation from adjacent channels will result.
Frank

 

[sanketachari]

Thanks.

Actually I was testing the model for 700 MHz - 900 MHz frequency range. I am still getting the warnings like 'More than 1 mixing term has landed on frequency 758 MHz ,800 MHz, 842 MHz'.

Can you suggest an ADS model for 'design of Double down conversion of superhyterodyne receiver' ? I am also unaware about the required parameters to be set. What changes should I do in the designed model to attain the goal ?

 

[biff44]

that is a fairly standard type of frequency range that cable tv tuners work over. They accomplish the reception, without any frequency holes, but using an first IF frequency > 1.1 GHz, THEN downconverting.

 

[0dBc]

As chuckey pointed out there are problems with your frequency plan. The general rule of thumb is that the IF frequency should be above the highest frequency to be received by at least 35%. In your case this happens to be 860*1.35=1161 MHz.

 

[vfone]

The old TV tuners (54 MHz to ~800 MHz) use an IF of about 420 MHz. This frequency gap was somewhere between VHF-III high band and UHF band, so the user didn't notice this gap.

 

[irisaru]

Hi,

For the frequency range 54MHz - 860 MHz, I have found that some papers use " Up/Down Conversion Architecture", the first IF is usually 1.2 GHz, and the second IF is 36/44 MHz. Could you please tell me why the call the 36/44 MHz is the standard IF?

Thanks

 

[chuckey]

From My first post, an IF of 38.9 Fv IF, is related to the image rejection when the RF input is in the range 450 -860 MHZ. So if you get hold of a TV, it will have the IF transformers and filters already fitted and tuned, though they will be set wideband to encompass 32 - 41 MHZ so the sound carrier can get through it.
I worked at a place where they designed and built the highest quality receivers for broadcast use (re-broadcast receivers and monitoring receivers), they actually chose an IF of 22.5 MHZ, giving easier filters BUT reduced image frequency rejection. This was because they were fixed tuned receivers, so the RF stages were operated with better filtering.
Frank

 

[biff44]

if it were me, I would pick a 1st LO of maybe 1.1 GHz, filter with a saw bpf, and then down convert to your output IF frequency. If you do the math, the image rejection and spurs will be much better.

 

[irisaru]

Thank you for your opinion,
I totally agree with you on IF of 22.5 MHz giving easier filters and reduce image frequency rejection. But my project is RF tuner design so I need a demodulator to decode the IF signal. The commercial product of demodulator IF input are usually 36/44 MHz, some of them are low-IF input. Therefore, I need to choose the IF of 36MHz

Irisaru