zero biased schottky detector problem - RF Cafe Forums
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Post subject: zero biased schottky detector problem Posted: Fri Aug 05, 2005 1:10 pm
I am sorry for the newbie question. RF is not my expertise and I need a few concepts to set up a small test bed.
I have designed a detector using zero biased schottky diode in voltage doubler configuration using Agilents HSMS 2852 package. I have mounted the SOT23 package along with relevant matching components on a 31 mils FR-4 board. I provide RF input throught a signal generator at 900 MHz using end launch SMA connectors. The output is measured using a Volt meter.
My problem, is that the measured performance is nowhere close to what is mentioned in the data sheet (which I also get on simulation). The output DC voltage is much lower that mentioned in data sheet at the input power levels. How can I go about "debugging" this problem?
Post subject: Zero-bias Schottky detectorPosted: Sat Aug 06, 2005 11:12 am
Please tell us a bit more about the operating conditions - like what is the RF voltage?
Voltage doubler circuits don't work too well in the square-law region, so you have to have enough voltage to get above it into the exponential region. In the case of Schottky diodes, one reason simulations sometimes are inaccurate is poor modeling of the diode capacitance.
Post subject: Posted: Sat Aug 06, 2005 7:06 pm
In the actual system, the detector will be working with power levels of 0dBm to -25 dBm.
However, right now, I am trying to test the performance of the detector circuit alone. I am varying the input power level and trying to reproduce the charecteristic shown in the data sheets and application notes.
For instance, application note 1089, shows that the DC output produced using the voltage doubler, at -30dBm, 900MHz input is about 30mV. On measurement for my detector i get output of only about 1 -2mV.
I am just unsure about where the problem might lie and to go about finding it.
Post subject: Voltage DoublerPosted: Sun Aug 07, 2005 7:44 pm
How does your circuit differ from the one in AN-1089, both schematically and physically?