Diode in opposite direction?
$begingroup$
Its really bothering me that the diode is shown in the opposite direction here and i don't understand why its been put like that? the input voltage will come from the left side of the circuit then why is the diode's cathode connected to the output of the op amp? does the polarity even matter here?
diodes radio receiver
asked Mar 24 at 15:36
HaidyEHaidyE
304
$endgroup$
add a comment |
$begingroup$
Its really bothering me that the diode is shown in the opposite direction here and i don't understand why its been put like that? the input voltage will come from the left side of the circuit then why is the diode's cathode connected to the output of the op amp? does the polarity even matter here?
diodes radio receiver
asked Mar 24 at 15:36
HaidyEHaidyE
304
$endgroup$
add a comment |
$begingroup$
Its really bothering me that the diode is shown in the opposite direction here and i don't understand why its been put like that? the input voltage will come from the left side of the circuit then why is the diode's cathode connected to the output of the op amp? does the polarity even matter here?
diodes radio receiver
asked Mar 24 at 15:36
HaidyEHaidyE
304
$endgroup$
Its really bothering me that the diode is shown in the opposite direction here and i don't understand why its been put like that? the input voltage will come from the left side of the circuit then why is the diode's cathode connected to the output of the op amp? does the polarity even matter here?
diodes radio receiver
diodes radio receiver
asked Mar 24 at 15:36
HaidyEHaidyE
304
asked Mar 24 at 15:36
HaidyEHaidyE
304
asked Mar 24 at 15:36
HaidyEHaidyE
304
asked Mar 24 at 15:36
HaidyEHaidyE
304
asked Mar 24 at 15:36
HaidyEHaidyE
304
304
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
In this particular circuit application, the demodulation of amplitude modulated RF, no, the polarity of the diode does not matter. If you reverse the diode, you simply track the positive part of the envelope rather than the negative part. Either will give you the demodulated signal.
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
$endgroup$
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
2
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
|
show 2 more comments
$begingroup$
At the point just before the first amp, the radio waves have been filtered to a particular frequency by L1, C1 & C2. That first amplifier is not an op-amp, it is an RF gain amplifier. It amplifies the incoming signal by a number of dB. The signal before and after will be an AC signal, equally biased around ground.
The diode or detector gets rid of one half of the signal (either the positive half or the negative half, depending on which way the diode is). Description of AM Detector.
The next stage filters off the carrier signal with a low-pass filter.
As the next amp, an op-amp has a bipolar power supply so it can handle either the positive or negative signal. It amplifies the sound waveform for the speaker.
edited Mar 24 at 20:41
SamGibson
11.7k41739
answered Mar 24 at 17:17
TpKnetTpKnet
1015
$endgroup$
add a comment |
$begingroup$
The signal into the diode is a (presumably) AM (amplitude modulated) signal. The variations in amplitude are what is of interest to the listener and are what the amplifier chain is seeking to recover.
As shown the diode rectifies negative going halves of the signal.
If reversed it would rectify positive going half cycles.
Either way, Cd provides a filter that smooths out (and so removes) the RF variations and results in a voltage that varies with the amplitude of the incoming signal. As shown you get negative variations which are smoothed. Reverse the diode and you would get positive going variations. The two are the same except inverted.
In either case the resultant "envelope" is AC coupled by Cb, and is DC ground referenced by Rb. So EITHER way "Amplifier" "sees" an AC signal centred around ground. This is amplified and, again, AC coupled vi C3 to the headphones.
So, either way the result is much the same to the end user.
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
$endgroup$
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
In this particular circuit application, the demodulation of amplitude modulated RF, no, the polarity of the diode does not matter. If you reverse the diode, you simply track the positive part of the envelope rather than the negative part. Either will give you the demodulated signal.
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
$endgroup$
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
2
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
|
show 2 more comments
$begingroup$
In this particular circuit application, the demodulation of amplitude modulated RF, no, the polarity of the diode does not matter. If you reverse the diode, you simply track the positive part of the envelope rather than the negative part. Either will give you the demodulated signal.
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
$endgroup$
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
2
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
|
show 2 more comments
$begingroup$
In this particular circuit application, the demodulation of amplitude modulated RF, no, the polarity of the diode does not matter. If you reverse the diode, you simply track the positive part of the envelope rather than the negative part. Either will give you the demodulated signal.
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
$endgroup$
In this particular circuit application, the demodulation of amplitude modulated RF, no, the polarity of the diode does not matter. If you reverse the diode, you simply track the positive part of the envelope rather than the negative part. Either will give you the demodulated signal.
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
answered Mar 24 at 15:42
Neil_UKNeil_UK
78.5k284181
78.5k284181
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
2
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
|
show 2 more comments
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
2
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
will the gain not make a difference then? we use three op amps.
$endgroup$
– HaidyE
Mar 24 at 15:43
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE no, I don't understand your comment. Neither gain nor number of opamps used makes a difference to the fact that inverting the polarity of the diode will not have a significant effect on the audio recovered from the RF signal, except that is, the polarity of the recovered signal.
$endgroup$
– Neil_UK
Mar 24 at 15:53
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
$begingroup$
@HaidyE Your RF "Amp" (between L1C2 and Diode) is an op-amp? A large portion of available opamps haven't much gain available for radio-frequency signals. Audio signals after the detector stage are considered low-frequency, and op-amps have lots of useful gain. That first amplifier really needs a large GBW product (gain x bandwidth)...if you use an op-amp, select carefully for this spec.
$endgroup$
– glen_geek
Mar 24 at 16:01
2
2
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
The RF amp may have a open collector output, so the diode would have to have its cathode facing the IC.
$endgroup$
– Sparky256
Mar 24 at 16:01
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
$begingroup$
i have used 3 op amps with a gain of 5 as i have mentioned before
$endgroup$
– HaidyE
Mar 24 at 16:07
|
show 2 more comments
$begingroup$
At the point just before the first amp, the radio waves have been filtered to a particular frequency by L1, C1 & C2. That first amplifier is not an op-amp, it is an RF gain amplifier. It amplifies the incoming signal by a number of dB. The signal before and after will be an AC signal, equally biased around ground.
The diode or detector gets rid of one half of the signal (either the positive half or the negative half, depending on which way the diode is). Description of AM Detector.
The next stage filters off the carrier signal with a low-pass filter.
As the next amp, an op-amp has a bipolar power supply so it can handle either the positive or negative signal. It amplifies the sound waveform for the speaker.
edited Mar 24 at 20:41
SamGibson
11.7k41739
answered Mar 24 at 17:17
TpKnetTpKnet
1015
$endgroup$
add a comment |
$begingroup$
At the point just before the first amp, the radio waves have been filtered to a particular frequency by L1, C1 & C2. That first amplifier is not an op-amp, it is an RF gain amplifier. It amplifies the incoming signal by a number of dB. The signal before and after will be an AC signal, equally biased around ground.
The diode or detector gets rid of one half of the signal (either the positive half or the negative half, depending on which way the diode is). Description of AM Detector.
The next stage filters off the carrier signal with a low-pass filter.
As the next amp, an op-amp has a bipolar power supply so it can handle either the positive or negative signal. It amplifies the sound waveform for the speaker.
edited Mar 24 at 20:41
SamGibson
11.7k41739
answered Mar 24 at 17:17
TpKnetTpKnet
1015
$endgroup$
add a comment |
$begingroup$
At the point just before the first amp, the radio waves have been filtered to a particular frequency by L1, C1 & C2. That first amplifier is not an op-amp, it is an RF gain amplifier. It amplifies the incoming signal by a number of dB. The signal before and after will be an AC signal, equally biased around ground.
The diode or detector gets rid of one half of the signal (either the positive half or the negative half, depending on which way the diode is). Description of AM Detector.
The next stage filters off the carrier signal with a low-pass filter.
As the next amp, an op-amp has a bipolar power supply so it can handle either the positive or negative signal. It amplifies the sound waveform for the speaker.
edited Mar 24 at 20:41
SamGibson
11.7k41739
answered Mar 24 at 17:17
TpKnetTpKnet
1015
$endgroup$
At the point just before the first amp, the radio waves have been filtered to a particular frequency by L1, C1 & C2. That first amplifier is not an op-amp, it is an RF gain amplifier. It amplifies the incoming signal by a number of dB. The signal before and after will be an AC signal, equally biased around ground.
The diode or detector gets rid of one half of the signal (either the positive half or the negative half, depending on which way the diode is). Description of AM Detector.
The next stage filters off the carrier signal with a low-pass filter.
As the next amp, an op-amp has a bipolar power supply so it can handle either the positive or negative signal. It amplifies the sound waveform for the speaker.
edited Mar 24 at 20:41
SamGibson
11.7k41739
answered Mar 24 at 17:17
TpKnetTpKnet
1015
edited Mar 24 at 20:41
SamGibson
11.7k41739
edited Mar 24 at 20:41
SamGibson
11.7k41739
edited Mar 24 at 20:41
SamGibson
11.7k41739
11.7k41739
answered Mar 24 at 17:17
TpKnetTpKnet
1015
answered Mar 24 at 17:17
TpKnetTpKnet
1015
answered Mar 24 at 17:17
TpKnetTpKnet
1015
1015
add a comment |
add a comment |
$begingroup$
The signal into the diode is a (presumably) AM (amplitude modulated) signal. The variations in amplitude are what is of interest to the listener and are what the amplifier chain is seeking to recover.
As shown the diode rectifies negative going halves of the signal.
If reversed it would rectify positive going half cycles.
Either way, Cd provides a filter that smooths out (and so removes) the RF variations and results in a voltage that varies with the amplitude of the incoming signal. As shown you get negative variations which are smoothed. Reverse the diode and you would get positive going variations. The two are the same except inverted.
In either case the resultant "envelope" is AC coupled by Cb, and is DC ground referenced by Rb. So EITHER way "Amplifier" "sees" an AC signal centred around ground. This is amplified and, again, AC coupled vi C3 to the headphones.
So, either way the result is much the same to the end user.
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
$endgroup$
add a comment |
$begingroup$
The signal into the diode is a (presumably) AM (amplitude modulated) signal. The variations in amplitude are what is of interest to the listener and are what the amplifier chain is seeking to recover.
As shown the diode rectifies negative going halves of the signal.
If reversed it would rectify positive going half cycles.
Either way, Cd provides a filter that smooths out (and so removes) the RF variations and results in a voltage that varies with the amplitude of the incoming signal. As shown you get negative variations which are smoothed. Reverse the diode and you would get positive going variations. The two are the same except inverted.
In either case the resultant "envelope" is AC coupled by Cb, and is DC ground referenced by Rb. So EITHER way "Amplifier" "sees" an AC signal centred around ground. This is amplified and, again, AC coupled vi C3 to the headphones.
So, either way the result is much the same to the end user.
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
$endgroup$
add a comment |
$begingroup$
The signal into the diode is a (presumably) AM (amplitude modulated) signal. The variations in amplitude are what is of interest to the listener and are what the amplifier chain is seeking to recover.
As shown the diode rectifies negative going halves of the signal.
If reversed it would rectify positive going half cycles.
Either way, Cd provides a filter that smooths out (and so removes) the RF variations and results in a voltage that varies with the amplitude of the incoming signal. As shown you get negative variations which are smoothed. Reverse the diode and you would get positive going variations. The two are the same except inverted.
In either case the resultant "envelope" is AC coupled by Cb, and is DC ground referenced by Rb. So EITHER way "Amplifier" "sees" an AC signal centred around ground. This is amplified and, again, AC coupled vi C3 to the headphones.
So, either way the result is much the same to the end user.
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
$endgroup$
The signal into the diode is a (presumably) AM (amplitude modulated) signal. The variations in amplitude are what is of interest to the listener and are what the amplifier chain is seeking to recover.
As shown the diode rectifies negative going halves of the signal.
If reversed it would rectify positive going half cycles.
Either way, Cd provides a filter that smooths out (and so removes) the RF variations and results in a voltage that varies with the amplitude of the incoming signal. As shown you get negative variations which are smoothed. Reverse the diode and you would get positive going variations. The two are the same except inverted.
In either case the resultant "envelope" is AC coupled by Cb, and is DC ground referenced by Rb. So EITHER way "Amplifier" "sees" an AC signal centred around ground. This is amplified and, again, AC coupled vi C3 to the headphones.
So, either way the result is much the same to the end user.
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
answered Mar 25 at 5:54
Russell McMahonRussell McMahon
118k9165296
118k9165296
add a comment |
add a comment |
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