real life method to properly biasing an amplyfier

[yefj]

Hello ,I have the following amplifyer PMA5-83-2W+ link shown below.
I am building a sequencer for this device.The problem is that i dont have any data regarding what will be the Load .
I dont have any model, The data sheet doesnt say what is the equivalent gate and drain loads.
The manufacturer doesnt have any answers.
So I suppose I am not the first person who doesnt have any simulation model of the amplyier and manages to design a sequencer for it.
Is there some methods I could use?
Thanks.

https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

 

[BradtheRad]

There is voltage-amplification and there's current-amplification. One caption on the data sheet mentions the unit is ideal for providing 12V @ 400mA. About 1/2W. The description says 2W but it's a good idea for you to stay under that limit. Say with a load with resistance (and/or combined with impedance) of 24 ohms.

I don't think I'd use it for driving a hi-fi speaker. Usually I've seen speakers drawing maybe 1VAC. Line level itself is 1-2V with weak A. So I chiefly want current amplification rather than voltage amplification.

Your power amplifier seems to have specialized features. It runs at 12V amplitudes. The data sheet describes uses for it which are very different from hi-fi. Up to 10GHz.

 

[dick_freebird]

Where is your schematic for the application? Who set you this task without this one thing?

 

[yefj]

I am building a sequencer as shown bellow but its tought to build a simulation without knowing what are the loads for Vg1 Vg2 and Vdd.
Anything could be done?
Thanks.

 

[FvM]

Amp datasheet gives an idea of load characteristic, max. 4 mA Vgx, 400 mA Vd.

 

[yefj]

Hello , I have an amplyfier called PMA5-83-2W+.
Looking at the sequence bellow I understnad that I need 3 pulses.
first pulse:
0 to -12 (which will be converted to -2V) for Vg1 , (m12 signal on the plot).
after first pulse comes a second pulse
0 to +12 (which will be converted to +5V) for Vg2 (Vq1_c on the plot)
after the second pulse comes the third pulse.
0 to +12 for VDD. (out2 on the plot)
LTspice file is attached.
I need to have a very low impedance on each of the outpruts of this circuit so the signal will be delivered very well to the ampylifer.
How do you reccomend to implement it.
I know i Can use a voltage divider,regulator ,tuned reference,zenner.
I know I should use an OPAMP but i dont know how?

any ideas will be great.
Thanks.
https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

 

[BradtheRad]

I know i Can use a voltage divider,regulator ,tuned reference,zenner.
I know I should use an OPAMP but i dont know how?

Simple method... The 3914 IC activates its outputs in response to the one incoming voltage. The turn-off sequence activates in reverse order as input voltage falls.

Or, build a multiple opamp window comparator. Raise the one incoming voltage to activate circuits in sequence. Reduce incoming voltage to produce reverse sequence.

You'll still need robust transistors to handle Ampere needs.

 

[D.A.(Tony)Stewart]

Your method is like driving a cart before the horse. The horse was your Yig tuned Osc for 12GHz (?) Radar paper block diagram and since you have no successful experience with that, you are trying to figure out how to enable the power switch without awareness of the surge or disturbances and details or even how to read a datasheet for OpAmps and FETs.

In layman’s terms you are trying to run while you don’t yet know how to walk and you have been crawling for 8 months here on basic issues without a purpose. (Design Specs)

I and many others have advised you to start from Design Specs with an end goal. But start with simpler goals not X band when you could not understand audio band CC driver at 10kHz .

So start over by learning all the prerequisites of component applications interpreting specs for BJTs FETs linear ICs small scale logic(SSL), PLA’s.

Alternatively jump right into Object Oriented Programming that @dana has been sharing with the group while reading and practise simple tools he has shared.

I struggled for many years starting out but my 1st 3 month design was VLF Doppler relatively simple analog-digital but I had a deadline to meet. If you love the world of Analog electronics you will find a way to accelerate your craft. All the info is out there in the web. You just have to know where to look and how to search.

 

[yefj]

Simple method... The 3914 IC activates its outputs in response to the one incoming voltage. The turn-off sequence activates in reverse order as input voltage falls.

Or, build a multiple opamp window comparator. Raise the one incoming voltage to activate circuits in sequence. Reduce incoming voltage to produce reverse sequence.

You'll still need robust transistors to handle Ampere needs.

Hello Brad,regading the needs:
1.I can use a zener diode method to lower -12V into -2V as shown below.
Is it a proper method?
2.when we talk regarding the current needs then we need to put a load on that output.
given the table below should I use R=0.8/15uA correct?
3.How do i know what current needs to flow into the load?
Thanks.

https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

 

[BradtheRad]

Instead of a zener diode you might try a plain red led, if Amperes carried is small. Its fwd voltage is 1.8V or so. Put a low-ohms resistor in series to add a few tenths of a volt.

If A is large, then consider putting a few diodes in series.

The reason for these recommendations: I don't think you'll find any 2V zener diode. Well maybe for some expense compared to the standard series.

--- Updated Sep 8, 2024 ---

3.How do i know what current needs to flow into the load?

Current flowing out of the device (therefore into the load) has to be present in the supply rails. Obviously the positive polarity waveform comes from the positive voltage supply into the device.

However negative output flows from the load into the device therefore negative current flows out of its pin 13 from what I can see, to the negative polarity supply rail.

The amount of Amperes sunk or sourced from the device can change quickly in normal operation. Since your device has the op amp icon, I think you can assume it behaves like an op amp: Its output pin presents the correct voltage to the load no matter what the load is (within reason). The output circuitry which can do this has to be the result of genius design. Your load should not source or sink too much Amperes. In terms of Watts (or volt-Amps) it should not go over 2W for any instant. While experimenting I would grip the device between my fingers and turn down the Watts used if I feel it burning. What burns my fingers? 0.7 Watt average.

 

[D.A.(Tony)Stewart]

None of your questions has shown you are following instructions to define specs first. Read about basic properties of impedance, gain and offset. You are wasting time choosing parts before specs. Like offset of an LT1080 then you want to use a Zener with much larger offset tolerance.

Find out how it must behave with tolerances and list these specs 1st for everything that matters.

 

[yefj]

Hello Brad,As you can see in the last stage of the schematics presented below, I have succeeded in converting the -12V into a -2.5 as shown below.
I used a comparator with constant voltage which is passing M12 signal, then using TL431 i converted -12V to -2.5V.
I know that choosing comparator is because we want low impedance.
How can i know according to the datasheet if this signal will fit good the component?
Full LTspice simulation is attached.

https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

 

[BradtheRad]

using TL431 i converted -12V to -2.5V

I've never seen a negative polarity applied to TL431. Is it made to sink current? Is there such a thing as a negative version of TL431? In the case of negative circuitry you must re-think and revise your approach.

The location of your 0V ground becomes important.
The direction of electron travel (or current bundle travel) must dictate your selection of devices.

Example, notice manufacturers have a series of 79xx voltage regulators because we can't use 78xx series in negative territory.

 

[yefj]

Hello Brad,Yes I understand .JUst for the sake of the analog logic the circuit is working as shown in the simulation.
How can I know if The output of this circuit in post 12 will be delivered to Vg1 ?
Again i dont know what load i need to put?

All I know i put -2.5V to Vg1 and i dont know how to understand if its the signal that my Vg1 is looging for, load capacacitance is uknown.
Load resistance is uknown.
Thanks.

https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

 

[BradtheRad]

Again i dont know what load i need to put?

load capacacitance is uknown.
Load resistance is uknown.
Thanks.

* The description tells how the device amplifies a wide spectrum of frequencies, up to 10 GHz. I believe its output is suitable to send to an antenna. (50 ohm impedance is cited which is conventional in rf equipment.)

With such versatility it's easy to change the frequency of transmission and tune your antenna to match. Thus your circuitry is not limited to operating on one frequency or narrow band of frequencies. I saw an old-timer remark how any HAM can reach a long distance with 1/2 Watt by using the proper tuned antenna.

* From the datasheet it seems that Vg1 should startup at -2V, then you adjust it manually while operating. I believe you need a flexible circuit rather than TL431.

 

[yefj]

Hello Brad,I have built the feeding of Vg1 as shown below.
Basickly the comparator is just passing M12 signal because 4>0 always.
Why cant I just use TL431 to convert M12 directly into -2.5, why do I need to use this OPAMP also?
I know perfectly that the circuit i was given in the begining is very faulty so i am looking for logic.
Is there such a thing in using OPAMP? why not just use only the TL431 regulator?
Thanks.

 

[BradtheRad]

Why cant I just use TL431 to convert M12 directly into -2.5, why do I need to use this OPAMP also?

Even by turning the TL431 upside-down I don't think it works correctly to yield -2V at the Amperes your device requires.

I also believe the datasheet calls for manual adjustment of the negative supply (-2v).

Usual schematics show a resistor divider at the TL431 reference terminal.

This 3-window comparator can be modified to provide your turn-on sequence.

Link below runs my schematic in the animated interactive simulator at falstad.com/circuit. The led's point to the right. Notice they light in sequence, then turn-off in reverse sequence.

tinyurl.com/29brhenf

 

[yefj]

Hello Brad , I think i understand .
I need to know how much current the reference can sink ( negative voltage) without ruining the -2.5V value or burning.
How can i test it in My LTspice simulation I attached.
.


LTspice simulation files are attached.
"Even by turning the TL431 upside-down I don't think it works correctly to yield -2V at the Amperes your device requires."

 

[D.A.(Tony)Stewart]

OK again you have failed to define spec for low impedance and voltage regulation error.

Your design approach is no good.

A) Either define load current max and load regulation error % @ -2.5V
e.g. 1% of 2.5V / 1A =Zo = 25 mohms at DC and rising to ___ at ___ MHz
Or
B) Define Zo at DC, f(max) based on fmax=0.5 / Trise time
A comparator output impedance Zol = output low = Vol/Io with open switch has R pull-up for Zoh

If this is just gate current then DC is negl. and ac current depends on switched Q when Vdd is enabled unless RF is involved on gate input then Ciss Rg +Rs, Vgs swing may be used to compute gate current.

 

[yefj]

Hello ,I understand that the value of the load is irrelevant.
Whats relevant is the ability of the circuit bellow to sink current while keeping the desired -2.5V
When I swept RLoad for different value and i see that at some Rload values i get 8mA(twice the maximal rating)
How do i know that it will get enough current from my reference regular source ?
Could you say why exactly its not going to work,as i see it in the simation i get 8mA for -2.5V for 800 ohm load?
LTspice file is attached.
Thanks.