Sawtooth wave generator circuit (2)

All kinds of sawtooth voltage generators have in common the use of capacitor charging. The discharge function produces the forward and reverse paths of the sawtooth wave voltage. The
simple sawtooth wave voltage generator circuit is simple, but the linearity of the output sawtooth wave voltage is very poor. The voltage amplitude changes exponentially with time, deviating
seriously from linearity, and the power supply utilization rate is not high. To obtain a sawtooth voltage with good linearity, the key is to try to
maintain a constant current charge on the capacitor during the scanning period. This is the basic starting point of the constant current source sawtooth voltage generator. The constant current transistor uses a common-base connected transistor
to emit a current J. At a certain time, the collector current is basically unchanged,
and the linear scan is achieved by maintaining the constant charging current of the capacitor . However, when the transistor in the constant current circuit
is in a saturated state as the scan voltage amplitude changes, the scan voltage will no longer change, and the output
voltage waveform will appear flat-top. Therefore, in this circuit, the output amplitude has certain
limitations. , the maximum amplitude v<,rhn can only be Qiu-Ut.
    In order to prevent the scanning wave from being flat-topped and distorted, the optimal period of scanning (i.e. the maximum
scanning period) 1. It should be the time required to charge the capacitor until the output of the transistor VT1 reaches the maximum
amplitude . The circuit is as follows As shown in the figure. The scanning period (Tp), rest period (z,) and period (n) of the
    separately excited sawtooth wave generator
depend on the rest period, pulse width and period of the input signal. Only
the retrace period of the generator is determined by the circuit itself. Determined by parameters.