anyone have a pin diode linearizer schematic handy?

[biff44]

Been searching around and did not find a simple schematic, and I'm too tired to reinvent the wheel! Need to take 0 to +10 V control in, and drive 4 microwave pin diodes spaced quarter wave apart to get a linearized Vin vs. dB attenuation. Will take either a breakpoint linearized or log driver.

Thanks, Rich

 

[tony_lth]

Here is HSMP-3816 Application. I don't know whether it will help you or not.

 

[biff44]

No Tony, I am looking for the op amp driver circuit that drives the microwave portion.

I did find this one:

**broken link removed**

The last diagram on the page looks promising, but it looks unnecesarrily complex. I was hoping to do the same thing with one op amp and one transistor! That diagram also probably needs some speed-up capacitors around the output transitor.

Rich

 

[tony_lth]

maybe you can use HMC346 and ...

 

[ledum]

Do you mean something like this?
Sign under the figure in Russian means: the schematic of the absorbing ladder type attenuator with a certain law of change of diodes resistance.
Left connector is input.

 

[biff44]

Yes Ledum, that is the microwave structure I am trying to drive. I have 4 pin diodes, and they are all fed from one common bias point. I need to take a control voltage input, and convert it to a diode driving current so that dB Insersion Loss is propostional to Vcontrol input.

Tony, that is a good circuit, but the HMC device is a FET based switch (voltage controlled), so I am not so sure that driver will work with a PIN diode attenuator.

 

[tony_lth]

Hi, biff44,
HMC346LP3 is a voltage-variable attenuator, I think if use HMC346LP3E, you don't need use PIN diode any more. Attached is HMC346 voltage vs. attenuation. But I don't know what's your requirement on phase.

 

[ledum]

We used topology like at attachment (alumina 0.5mm, resistors - tantalum thin film 50 ohms per square). Diodes were old soviet 2A533A-3 p-i-n diodes (all sizes in mm, Cd=0.05pF, Ubr=70V). Control law was very close to the linear. Regulation range at Vmod 0-12V (current 0-100mA) was 35dB for 4 diodes configuration in half-octave band near 12GHz. Loss at 0V control voltage was something like 1.5 dB. But, it was 25 years ago. I think tony_lth is right about HMC346LP3

 

[G0HZU]

maybe you can use HMC346 and ...

I have the above HMC346 + opamp circuit somewhere already milled onto a PCB. I tested this circuit a few years ago.

I don't recall it being that linear in terms of Volts vs attenuation. Also the control V vs attenuation was a bit iffy over temperature on the higher attenuation settings.

But it was still a useful attenuator

 

[tony_lth]

I guess biff44 need control circuits between detector and attenuators, not RF circuits.