# High Frequency Rectification

I am trying to monitor an incoming signal and get some properties from it. The signal is a sine wave +-5V at 900Mhz. I am trying to measure the amplitude and the frequency of the signal. I will probably also have to buffer the input but that shouldn't be to much trouble.

I have been able to use schottky rectification for a couple of Mhz but eventually the diode cant recover fast enough. If anyone has any suggestion of small signal diodes that might be able to keep up with this that would be great. I have also looked at some switchable pre-scalers but unfortunately I loose the ability to feed my RC network.

As far as measuring the amplitude goes I am feeding the rectified circuit into an RC network.

• What papers have you studied on the topic of RF rectification? For example, have you considered the use of DC-boosted bias CMOS rectification? There is a lot on the topic. – jonk Mar 1 '18 at 0:17
• How does rectification relate to trying to measure the amplitude and frequency? Are you trying to make an RF detector (part of an RF power meter)? – The Photon Mar 1 '18 at 1:44
• I should have mention that. The output of the rectification is going to a frequency divider and then to a counter on an FPGA. The amplitude will be going to the ADC. It does not need to be monitored at a high frequency. – Meozaa Mar 1 '18 at 2:53
• Why rectify (doubling the frequency) and then divide the frequency again? Why not just ac-couple, re-bias, and limit (if necessary) to drive a counter's clock input? What is the range of input amplitudes you need to be able to handle? – The Photon Mar 1 '18 at 4:26
• The lowest amplitude will be 300mv and the highest will be 4v – Meozaa Mar 1 '18 at 16:28

The task of measuring an amplitude of a powerful RF signal is usually accomplished by means of so-called "demodulating logarithmic amplifier", or "RF power detector". An example would be LTC5505, ADL5505, AD8313, or similar. Usually the RF transmission line has either a high-impedance DC-blocking decoupler,

or a directional coupler based on stripline technology:

The output of the RF detectors is usually used as a feedback for RF power generator, to maintain stable power level of transmission.

To measure the frequency you would need an additional block. You need to fork the signal into an small RF amplifier and use a fast counter.

Pin Diode:

You may be able to modify a coupling connector or splitter , stripline directional coupler (DC3) to connect the peak detector and buffer to a DMM.

<1 ohm pin diode into a 1~3pF FET buffer.

You can adjust the impedance to choose your calibration factors for desired load. ( e.g. 50 Ohm)

https://www.nxp.com/products/rf/rf-discrete-components-low-power/rf-diodes/pin-diodes:MC_42530

• okay perfect. Ill get a spice model for these and see how it goes. – Meozaa Mar 1 '18 at 3:56

Just as a follow up my solution was to use an LTC5507 RF peak detector IC. This took out the work of temperature compensating a diode and tuning the range of the system.

The downside to this method is that you cannot select what frequency you are trying to target. This device also requires a low pass or band pass filter for the best results.