Forum: Analog Circuits Analog signal interfacing to ADC

 Author: Milruwan Perera (Company: Student) (milprasad) Posted on: 2014-01-12 10:38
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I tried to interface a FM multiplex signal through an transistor
amplifier to ADC.Then I tried to convert the sampled signal to an analog
signal and observed the output through oscilloscope. But the observed
output was distorted. Then I give a 400mV signal from signal generator
and amplified it to 5V. The amplified signal is then given to the ADC
observed the DAC output.But the observed output is distorted. But when I
give the 5v sinusoidal signal from signal generator directly to the ADC
and observe the DAC output,Then I can observe a waveform similar to the
input.

1)I think there is a issue with the amplifier's output impedance. Is my
assumption correct?
2)How to overcome this problem? (since the FM mux output is 500mV I need
to use an amplifier)
3)How to increase the amplifiers output impedance?

: Edited by User
 Author: Milruwan Perera (Company: Student) (milprasad) Posted on: 2014-01-16 09:26
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Here is the circuit I had tested(img 1).
When I give an analog signal I can get the emitter follower output as
follows. (Yellow - output , Blue -input)(img 2)
After giving the emitter follower output to the ADC and observe the DAC
output from oscilloscope,I can observe a distorted signal as
follows(yellow).
(img 3)

How to get the original signal from the ADC?
What are the modifications I need to do?

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