# frequency limit of of SCHOTTKY bridge Rectifiers

Discussion in 'General Electronics Chat' started by rentiantong123, Oct 13, 2015.

1. ### rentiantong123 Thread Starter New Member

Mar 29, 2014
23
1
I using bridge rectifiers to convert RF signal to DC. It seems common bridge rectifiers cannot work in high frequency condition like higher than 200MHz. So I used schotty bridge rectifiers for their fast recover time. But from datasheet I didn't find the exact frequency limit but only a figure of forward current vs Number of cycles at 60Hz. Can anyone tell me what does this figure mean? And how can I know the upper limit frequency?

2. ### crutschow Expert

Mar 14, 2008
13,503
3,376
Schottky diodes are very fast (small ones are used at microwave frequencies) so the usual limit is just the junction capacitance, which causes current feed-through at high frequencies.
Smaller diodes have less capacitance so you probably want to use a small one rated for RF detection.

The forward current versus number of 60Hz cycles is likely related to the surge current rating and has nothing to do with frequency response.

3. ### rentiantong123 Thread Starter New Member

Mar 29, 2014
23
1
Thanks! All I can find is single diode. Do you know any rectifiers which can run in 400Mhz @ lower than 1A?

4. ### Bordodynov Active Member

May 20, 2015
673
194
I have long been interested in the performance of Schottky diodes.
Usually the spice model for Schottky diodes tt parameters is not specified. Default tt=0. But for some diodes is tt=5ns or even tt=20ns.
Very good diodes from mf. Agilent: HSMSxxxx.
To the right advice, we need to know the parameters of your signal.
Use Spice (LTspice).

5. ### Bordodynov Active Member

May 20, 2015
673
194
I do not know how you use voltage. Here's a good diode for high voltages C3D02060 (Vrrm=600V,If(avg)=2A). Disadvantage: large voltage drop (1.2V).
.MODEL CSD01060 D IS=22.008E-18 N=1.0313 RS=.34849 IKF=65.284 CJO=118.40p M=.39104 VJ=.46094 ISR=372.48n NR=4.4145 BV=800.13 IBV=.12955 TT=21.668p MFG=Cree TYPE=schottky
.

Last edited: Oct 13, 2015
6. ### crutschow Expert

Mar 14, 2008
13,503
3,376
You can make 4 diodes into a bridge.
How much current do you actually want to rectify?
What is the source of this high current @ 400MHz?

7. ### rentiantong123 Thread Starter New Member

Mar 29, 2014
23
1
Thanks!The input power is fairly small (around 5W) and the RMS DC voltage should be around 8v-10V, I don't know how exactly to calculate the current but it should be less than 500mA.
The rectifier I use is MB14S from Micro Commercial Components: http://www.digikey.com/product-detail/en/MB18S-TP/MB18S-TPMSCT-ND/5114037
It's a Schottky diode bridge. It doesn't have a frequency rating on datasheet but I think it should work on 400Mhz.

8. ### rentiantong123 Thread Starter New Member

Mar 29, 2014
23
1
The input is decoupled 400Mhz RF power (around 5W). Current should be less than 500mA.
Do you think MB14S from Micro Commercial Components: http://www.digikey.com/product-detail/en/MB18S-TP/MB18S-TPMSCT-ND/5114037 works?

9. ### crutschow Expert

Mar 14, 2008
13,503
3,376
The junction capacitance of the MB14S is over 100pF, giving a reactance of less than 4Ω at 400MHz.
It will thus likely not work well as a rectifier at that frequency.

You need a diode with a much lower capacitance.

The diode current will depend upon the load. What is that load?
It's this large current that makes finding a proper diode difficult for those frequencies..

10. ### rentiantong123 Thread Starter New Member

Mar 29, 2014
23
1
Thank you so much for explaining this for me. Engineer from Micro Commercial Components told me the frequency should not be higher than 60MHz. I may need to find a new rectifier with lower capacitance.
What I still don't understand is why diode doesn't work under low impedance. Is there anywhere I can find more information about this?

11. ### crutschow Expert

Mar 14, 2008
13,503
3,376
I don't understand what you don't understand.
A diode with a high (parallel) capacitance will conduct the signal through it in both directions, so it doesn't act as a very good rectifier.

Last edited: Oct 15, 2015
cmartinez likes this.
12. ### Tesla23 Active Member

May 10, 2009
323
67
Interesting problem. I've never built one, but here's a paper where they claim to get 78% efficiency rectifying a 43dBm (20W) 920MHz signal using 8 HSMS2702 diode pairs (from Table II in the paper). It provided the power into 10ohms, so that means more than 10V across the load.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6384845

Mar 29, 2014
23
1