How to connect these 2 circuits to...

Thread Starter

eman12

Joined Oct 26, 2007
41
Hi,
I am a newbie here,

Can someone help me and say me how to connect the output of the '1' circuit to the input od the '2' circuit?it does not work when I simply connect the wires together?!

thanks in advance.
 

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beenthere

Joined Apr 20, 2004
15,819
The modilator is going to produce some signal with a carrier frequency and a modulation form some source. It will have excursions above and below ground, which makes it unsuited to act as a drive sognal for the digital hex inverter.

To echo Thingmaker3, what are you trying to do???
 

Thread Starter

eman12

Joined Oct 26, 2007
41
The modilator is going to produce some signal with a carrier frequency and a modulation form some source. It will have excursions above and below ground, which makes it unsuited to act as a drive sognal for the digital hex inverter.

To echo Thingmaker3, what are you trying to do???
Thanks,

I want to amplify the output of the modulator by a BRIDGE amplifier.
I don't like and do'nt need to use a power amplifier to do so. my amplified signal is going to drive just an ultrasonic sensor.

I just knew the '2' circuit as a simple and BRIDGED low signal amplifier.

So what do to?
Are you sure I am not able to drive the out put of the modulator with that amplifier?
 

thingmaker3

Joined May 16, 2005
5,084
The inverter chip (IC3 of "circuit 2") will treat anything below about 2.5 volts as "low" and anything above 2.5 volts as "high."

It is not an amplifier. Well, I suppose one could class it as a current amp, but it is strictly digital in nature.

Why not use an OpAmp?
 

Ron H

Joined Apr 14, 2005
7,014
A digital driver will cause you to lose your modulation information, even if you could get the correct input voltage levels. You need op amps. See below.
You probably won't like the choice of op amp, but you need one that can drive a capacitive load with high output current.
CAVEAT: I have not tested this circuit, or even simulated it.
 

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Thread Starter

eman12

Joined Oct 26, 2007
41
A digital driver will cause you to lose your modulation information, even if you could get the correct input voltage levels. You need op amps. See below.
You probably won't like the choice of op amp, but you need one that can drive a capacitive load with high output current.
CAVEAT: I have not tested this circuit, or even simulated it.
Oh Thanks Sir,
I did not know that

I thought that the solution is an OP-AMP, but I had to and now have to make the whole circuit with a single ended supply while an op amp requires dual supply.

I am not sure of finding the LM8272 in my place so is there any alternative?

Can you say me why I was not able to amplify the output of mc1496 (pin 6)
with a transistor? I tested the darlington, class A.. etc.. but I could not to amplify the output of the modulator and there was not any signall at the output of the transistor!? an amplification with factor 2 or 3 was ok but the transistors were not on...

Thanks
 

Ron H

Joined Apr 14, 2005
7,014
Op amps do not necessarily need dual supplies. As you can see, the circuit I drew has only one.
You might be able to use a different op amp, but you should probably put 100 ohms in series with the transducer in order to isolate the capacitive load of the transducer from the op amps. LM8272 is specially designed to be able to drive capacitive loads.
A discrete transistor driver would be complex. If you want a bridge driver, both transistor amplifiers would need to be push-pull.
 

Thread Starter

eman12

Joined Oct 26, 2007
41
Op amps do not necessarily need dual supplies. As you can see, the circuit I drew has only one.
You might be able to use a different op amp, but you should probably put 100 ohms in series with the transducer in order to isolate the capacitive load of the transducer from the op amps. LM8272 is specially designed to be able to drive capacitive loads.
A discrete transistor driver would be complex. If you want a bridge driver, both transistor amplifiers would need to be push-pull.
I thought perhaps it is Single ended orginally. I used an onpamp with virtually grounded circuitry but the output signal was not the simallar as the output of the modulator.
Are yoy thinking that TL072 will work in replace to lm8272 without any modification?

No I just wanted to use 1 or 2 transistors in ordinary circitry to amplify the output of the modulator for the main amplifier, but the transistors did not work at all!
 

Ron H

Joined Apr 14, 2005
7,014
TL072 should probably have 100 ohms added in series with the transducer to prevent oscillation. You will get a lower maximum peak-to-peak output swing, and probably less current drive. All this means you will probably get less power out of your transducer. Of course, without knowing the specs of your transducer, and how much drive it needs, this entire amplifier is just an educated guess.
 

Thread Starter

eman12

Joined Oct 26, 2007
41
What kind of transistors did you use? And how were they connected? (What type of bias, et.al.?)

I use bc517 as a darlington transistor and then went to 8550 with different biasings.

which kind of circuity is able to work?

Ron, the opamp circuit you have designed is working thanks for it, but the output amplitude is low, how to get a higher amplification?

Sorry I am an
amateur in electronics field.
 

Ron H

Joined Apr 14, 2005
7,014
Ron, the opamp circuit you have designed is working thanks for it, but the output amplitude is low, how to get a higher amplification?

Sorry I am an
amateur in electronics field.
What value did you use for Rf?
What is the carrier frequency in your modulator?
 

Thread Starter

eman12

Joined Oct 26, 2007
41
What value did you use for Rf?
What is the carrier frequency in your modulator?
as I am using on the shelf transducers so the carrier freq is 40kHz.

Rf is between 100k to 330k but the amplitude is abit higher with 330k.

by the why there is not senseable difference in the output using a 100ohm resistor for the transducer.

Can you simulate the circuit and see if it is possible to imporveits output?

thanks
 

Ron H

Joined Apr 14, 2005
7,014
as I am using on the shelf transducers so the carrier freq is 40kHz.

Rf is between 100k to 330k but the amplitude is abit higher with 330k.

by the why there is not senseable difference in the output using a 100ohm resistor for the transducer.

Can you simulate the circuit and see if it is possible to imporveits output?

thanks
I ran a sim, and it works, but before I post results, tell us:

1. What is the frequency range of your modulating signal?
2. What is the source impedance of your modulating signal and your carrier signal?
3. Do you have a part number for the transducer, or better yet, a datasheet?
 

Thread Starter

eman12

Joined Oct 26, 2007
41
I ran a sim, and it works, but before I post results, tell us:

1. What is the frequency range of your modulating signal?
2. What is the source impedance of your modulating signal and your carrier signal?
3. Do you have a part number for the transducer, or better yet, a datasheet?
1. It is between 2 to 5kHz, why this factor is important?
2.I don't know how to calculate it!
3.See the files.

Do you know another brands for those capacitive opamps? I want to see If I can find another mark..

Thanks.
 

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Ron H

Joined Apr 14, 2005
7,014
1. It is between 2 to 5kHz, why this factor is important?
If it were low (such as 100Hz), the input RC would roll off the frequency response.
2.I don't know how to calculate it!
It is important, because your input impedances to the modulator are 100 ohms and 51 ohms, respectively. They may load your sources, severely attenuating the voltages. You either need low impedance sources, or we need to change the values of these resistors. What circuits do these signals come from?
3.See the files.
I tried to model the transducer as best I could. The equivalent circuit is on the attached schematic.

Do you know another brands for those capacitive opamps? I want to see If I can find another mark..

Thanks.
I think TL072 will be fine. The impedance of the transducer at resonance is high enough that 100 ohms in series will not reduce the output power significantly.

Note the voltage levels on the modulator and carrier voltage sources in my schematic. These are maximum peak voltages (from zero to peak). The maximum carrier level can be higher (0.5v peak?) if you don't mind having lots of carrier harmonics delivered to the transducer (it probably won't hurt anything). If you exceed the modulating input level, you will get lots of distortion in the modulation.
I hope you realize this is a balanced modulator with suppressed carrier output. It is not an amplitude modulator, although it could be modified if necessary.
 

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Thread Starter

eman12

Joined Oct 26, 2007
41
If it were low (such as 100Hz), the input RC would roll off the frequency response.
It is important, because your input impedances to the modulator are 100 ohms and 51 ohms, respectively. They may load your sources, severely attenuating the voltages. You either need low impedance sources, or we need to change the values of these resistors. What circuits do these signals come from?
I tried to model the transducer as best I could. The equivalent circuit is on the attached schematic.

I think TL072 will be fine. The impedance of the transducer at resonance is high enough that 100 ohms in series will not reduce the output power significantly.

Note the voltage levels on the modulator and carrier voltage sources in my schematic. These are maximum peak voltages (from zero to peak). The maximum carrier level can be higher (0.5v peak?) if you don't mind having lots of carrier harmonics delivered to the transducer (it probably won't hurt anything). If you exceed the modulating input level, you will get lots of distortion in the modulation.
I hope you realize this is a balanced modulator with suppressed carrier output. It is not an amplitude modulator, although it could be modified if necessary.
Thanks 'Ron H'

Can you post the pics in in a larger scale, so that I could see the values? I am not able to see the exact values but it seems you have changed them, are you want me to reflect these changes in my circuit?

As I know the 50k volume in the circuit is to null the carrier, this means if you turn it the carrier would insert in the out put and you will have the AM instead of suppressed carrier AM.

By the way, I want to incrase the source volatge to 17V and see if I am able to get more amplitude in the output of the op amp.
 

Thread Starter

eman12

Joined Oct 26, 2007
41
Oh, Ron H, I forgot to say that I have distortion at the output of TL072 when I increase the modulating amplitude or reduce the resistor between pin 2 and 3, so can you direct me or show me a circuit (probably based on transistors) to incrase the amplitude ofthe output of the modulator before TL072 and then reduce the volume of modulating signal or increase the Resistor? Is it possible at all?

Thanks
 
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