Transcript sample an analog input voltage

Sampling
Introduction

Sampling refers to the process of converting a
continuous, analog signal to discrete digital
numbers.
Sampling
Cont.,

When an analog voltage is directly connected to
the input of an ADC, the conversion process can
be affected if the analog voltage is changing
during the conversion time.
Sample and Hold circuit

The stability of the conversion process can be
improved by using a sample and hold circuit.

It is used to sample an analog input voltage for a
very short period of time and to hold the analog
voltage constant while the conversion takes place.
Sampling and Hold circuit
Sample and Hold circuit waveform
Sample and Hold circuit waveform

The waveform refers to the case of positive going
S/H pulses.

This circuit track the input signal when the
command is high and holds the input signal when
the command is low.
Ratio estimation of sampling survey animation
Sampling rate

The sampling rate is the number of samples of
data taken in one second for each channel of
audio being recorded.

CDs are recorded at 44,100 samples per second.
1000hz signal recorded at 8000 samples per
second sample rate
1000hz signal recorded at 44,100 samples per
second
Oversampling

Oversampling is the mathematical interpolation of
data.

It allows a signal with x number of samples/s to be
increased to any multiple of x. A 44k rate signal with 2
times oversampling will have 88,000 data points
from which to decode the recorded audio.
Oversampling
Sample and hold amplifier

The Op-amps A1 and A2 are worked as voltage
followers.

The output of A1 is connected to the input of
op-amp A2 through a switch.
Working of Sample and hold amplifier

The switch is controlled by a logic signal, meaning
that a high input ‘closes’ the switch and a low
input ‘opens’ it.

When the switch is closed, the capacitor rapidly
charges to Vin.
Sample and Hold Amplifier
Cont.,

Now the output of second Op-amp Vout is equal
to Vin.

When the switch opens, the capacitor retains its
charge.

Ideally, the output holds at a value of Vin.
Cont.,

If the switch is suddenly opened, the capacitor
voltage represents a sample of the input voltage
at the switch was opened.

The capacitor then holds this sample until the
switch is again closed and a new sample taken.
The End
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