TRF370417: Port iput impedance

Danilo A.

Part Number: TRF370417

Hi Team,

Our customer would like to clarify about the input impedance of TRF370417. According to our customer,

I'm using a couple of TRF370417 mixers in my design. In table 6.5 on page 5 of the data sheet it says that ZI(single ended) has an "input impedance, resistance" of 5 KOhms and an input impedance, parallel capacitance of 3 pF. So, is that saying that the port input impedance is not 50 Ohms? Also, in 8.1.1 on page 18 a bullet says "Terminate the ac-coupled LON with 50 ohms to GND. Does this mean hang a resistor on that port? What about LOP??? Isn't this port 50 Ohms??? How come your reference design shown in Figure 44 on page 19 don't have any of this? Which ports, if any, on this device that are NOT 50 Ohms across the specified operating band of the device?

Regards,

Danilo

over 1 year ago

0 Kang Hsia over 1 year ago

TI__Guru 66004 points

Hello,

The LO input ports have return loss spec of 15dB typical. This is with respect to 50ohm for each single ended leg (i.e. LON or LOP).

If you are driving this single-ended fashion, you may connect LON with 50ohm to ground, and connect another 50ohm LO source to LOP.

Or, you may connect a 2:1 balun to the LON/LOP and drive the the primary input with 50ohm source

Danilo A. said:
input impedance, resistance" of 5 KOhms and an input impedance, parallel capacitance of 3 pF.

The above statement is for baseband input (i.e. baseband I or baseband Q).

0 Roger Backhus over 1 year ago

Intellectual 410 points

Thank you.

0 Roger Backhus over 1 year ago in reply to Kang Hsia

Intellectual 410 points

Thank you. One more question if you will. Most mixers have isolation numbers for LO to RF and LO to IF. I don't see that on this chip's data sheet. I do see a parameter called "carrier feedthrough". I'm not sure exactly what that is. What is considered the "carrier"? Feedthrough to what? What is the LO to RF and LO to IF isolation on this part?

0 Kang Hsia over 1 year ago in reply to Roger Backhus

TI__Guru 66004 points

Hi Roger,

This is a quadrature upconverter, not a traditional mixer. This part have other parameters as performance metric.

Please see below for carrier feedthrough and optimization.

https://www.ti.com/lit/an/slwa046/slwa046.pdf

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TRF370417: Port iput impedance