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| promach:
In this paper 15.1 mW 60 GHz up-conversion mixer with 4.5 dB gain and 57.5 dB LO-RF isolation , I have three questions : 1) Have anyone designed a balun in spice software ? Is it doable ? 2) How to implement TL1 and TL2 (inductor implemented using transmission line) in spice software ? 3) How to derive the conversion gain expressions ((1) and (2)) for the up-conversion mixer circuit with and without negative resistance compensation in the paper ? |
| Paul Rose:
Question 1) only: I've never done this for 60 GHz, but you can make a balun in SPICE. For a 3 port balun, use three inductors. Set coupling between inductors with K statement: K1 L1 L2 L3 1 The 1 is the coupling. 1 is perfect, .9 is 90%, etc. This one K statement should be the same as the the following three statements ( in case your software only allows setting coupling between two inductors at a time ). K1 L1 L2 1 K2 L2 L3 1 K3 L1 L3 1 Use L1 as your unbalanced input ( ground one leg ). Observe phasing of L2 and L3. Connect "dotted" end of L2 to "plain" end of L3, and connect this common point to ground. Your balanced output is the "plain" end of L2 and the "dotted" end of L3. In LTSpice, for example, your inductor won't have a visible phasing dot until you add a K statement. Set the inductance to match the characteristics of the balun you are simulating. |
| promach:
--- Quote ---For a 3 port balun, use three inductors. Set coupling between inductors with K statement: K1 L1 L2 L3 1 The 1 is the coupling. 1 is perfect, .9 is 90%, etc. --- End quote --- Could you use a picture to explain your balun schematics structure ? By the way , see figure 3 of A 60‐GHz double‐balanced mixer with negative resistance compensation for direct up‐conversion using 90‐nm CMOS technology |
| Paul Rose:
Pic attached. Did this in a paint app, based on google pics of LTSpice. Don't have schematic editor on this linux laptop. Inserting the K statement makes the phasing dots show up ( at least in LTSpice ). Connect three inductors as shown. Pick ratio of inductance to model turns ratio of your balun ( impedance proportional to turns squared). Also pick inductance to set reactance according to your frequency. You want your inductive reactance to be a lot higher than the load impedance ( like 4 times or more ). I've never worked with anything higher than 500 MHz, but it does show the concept of a balun in spice. You don't have to use ground as the reference point. Whatever you connect to the center tap, the signal will be balanced with respect to that point. |
| promach:
Thanks for balun picture schematics But how do I interface your balun with mixer using differential current RF+ and RF- input signals ? By the way, someone else told me to use the following : but the load impedance for LO+ and LO- is almost infinite because it is mosfet gate ? |
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