Realistic sampling of signals:

Our goal of achieving a sampled signal is possible by the multiplication of the original C.T. signal with the generated train of pulses. Now these two signals are multiplied practically with the help of a multiplier as shown in the schematic below.  In our analysis so far, this is how we imagined sampling of a signal.

But impulses are a mathematical concept and they cannot be realized in a real system. In practice we can best obtain a train of pulses called a saw-tooth pulse. These pulses are generally used for creating a time-base for the operation of many electronic devices like the CRO (Cathode Ray Oscilloscope). 

Practical Implementation:

Lets see how the train of pulses of the following kind can be multiplied by a signal 'x(t)'.

Consider the circuit below.

The two pulse trains p₁(t) and p₂(t) are synchronized so that when one is high the other is low and vice verse as shown in the figure below:

In the circuit when x(t) and p₁(t)  are multiplied we get the output. Thus we get the output when p₁(t)  is ON and it is zero when  p₂(t) is ON.             

 You have just seen how we can multiply a signal x(t) with the following periodic pulse train p(t) to obtain the sampled signal . Now the train of pulses that we had used is shown below with respect to its amplitude and period.