A hysteresis type $$TTL$$ inverter is used to realize an oscillator in the circuit shown in the figure.

If the lower and upper trigger level voltages are $$0.9$$ $$V$$ and $$1.7$$ $$V,$$ the period (in $$ms$$), for which output is LOW, is ____________.

The transfer characteristic of the Op-amp circuit shown in figure is

The signal flow graph of a system is shown below. $$U(S)$$ is the input and $$C(S)$$ is the output.

Assuming $${h_1} = {b_1}$$ and $${h_0} = {b_0} - {b_1}{a_1},$$ the input-output transfer function, $$G\left( S \right) = {{C\left( S \right)} \over {U\left( S \right)}}$$ of the system is given by

The block diagram of a system is shown in the figure

If the desired transfer function of the system is $${{C\left( s \right)} \over {R\left( s \right)}}\, = {s \over {{s^2} + s + 1}},$$ then $$G(s)$$ is