| When a pulse passes through a capacitor the baseline must be
suppressed slightly in order to make the net area of the pulse above and
below the baseline equal. This is baseline shift and for a
succession of pulses may be significant.
The MCA will measure the height of the pulse relative to a fixed
voltage and so variations in the baseline to the pulse will cause errors
in the measured pulse height.
- To avoid baseline shift, such a baseline restorer circuit has
as its main purpose the return to zero of the baseline between pulses
in as short a time as possible.
- The use of baseline restoration also greatly reduces the effects of
low frequency disturbance such as power line hum and vibrational
microphonics which may be sent along the signal.
- The most effective type at high count rate is the gated restorer in
which the baseline is maintained at ground potential during the period
between pulses.
|
Baseline shift due to a regular series of identical
pulses. The total areas above and below the baseline are equal.
|
