Electrical – Voltage Multiplier – Cockcroft-Walton Capacitance Value

capacitancegsmmultiplierRFvoltage-regulator

I want to design a circuit in order to Harvest radio-frequency (RF) signals and get a DC Output to a specific load (i.e micro Watt Battery of a sensor).

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Notes to be considered :

  • input will be between (uV – mV) which is low.
  • frequency that i am harvesting from is the GSM frequency which is 900-915 MHz
  • considering this frequency value the capacitance should be really small (pico or nano farads)

During my research i have found that the most used step-up (In terms of Voltage) configurations are mainly three types which are :

1- Transformer Topology (Which is the cheapest and less efficient for such application)

2-Diodes : Rectifiers (Which I am not interested in due to losses)

3-Voltage Doubler/ Multiplier (Which consists of diodes and capacitors such like >> Cockcroft-Walton or any other configuration)

Now the thing is that there are a lot of types of the voltage multiplier, but I could not find any certain reference that can help me through the design of the Voltage multiplier.

For example how to calculate the capacitance values lets say for multi-stage multiplier with N Stages and Vin to Vout specific ratio ?

Such as :
Vin = 1V
Vout = 5V
N = 5-10 stages (or more depending on the output)

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Cockcroft-Walton Topology with 2 stages.

Any advice will be much appreciated

Best Answer

Start at a minimum of 10uW/cm² or -20dBm/cm² or 5 mV/mm E-field.

Needs impedance matched antenna complete circuit

Use a tuned rectangular patch antenna or rectenna with impedance matching network then smallest Cockcroft–Walton doublers into an open loop *with π/4 to π/2 radius..errhm I meant λ/4 to λ/2 radius... with suitable transmission line impedance matching striplines and at least 10 stages.

Need variable f generator

to measure s21 or DC out with f input

Another method is use Bennet doubler using e-VEH with a motion of 5mm_DA at low frequency ( e.g. 10~30 Hz) to demodulate the steady amplitude RF field.

Sch. Diodes must be low C and ESL

Low parasitic impedance: C< 0.05 pF, Ls < 0.2 nH

Dielectric substrate must be low loss tangent

like ceramic, teflon or special polyamide or https://plastics.ulprospector.com/datasheet/e120881/arlon-25n

must be small SMT for diode low pF for loop antenna

like 0201 SMD suitable for >>10GHz to prevent C divider loading and great efficiency.

Choose largest RF cap possible in smallest package e.g 0201 if possible.

  • use reputable suppliers with s parameters like Murata, TDK etc.
  • must be very low loss tangent NPO type material or better ceramic
  • Consider 50~100pF with much higher SRF.

Expect 1V at maybe >> -15dBm and 3.3V at -5dBm with > 10 stages

other

  • There is always an optimum limit to n- stage doublers based on impedance ratios and loads, leakage.

  • plan on $200 budget for proto unless you get free samples for all materials. (ha!)

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