Reverse of voltage control oscillator

I am looking at a circuit of my 'own' design:

^{simulate this circuit – Schematic created using CircuitLab}

Assuming that R1C1>>1/fsw1 we get:

When the switch is open:

\$ I_{r1} = I_{c1}\rightarrow \frac{V_{in}}{R_{1}}=-C_{1}V_{o}/(1-D)T \$

and when the switch is closed:

\$ I_{c1}=C_{1}V_{o}/DT\$

so we get that \$ V_{in}/R_{1} = C_{1}V_{o}/DT \rightarrow V_{o}/V_{in} = DT/R_{1}C_{1}\rightarrow \frac{V_{o}}{V_{in}} = \frac{D}{R_{1}C_{1}f_{sw}}\$

and because fsw>>R1C1 that means the equation becomes:\$ \frac{V_{o}}{V_{in}} = \frac{D}{f_{sw}} \$ so isnt this a direct frequency to DC voltage converter(or the reverse of a voltage controlled oscillator) or am I wrong?

Edit:

The voltage in the output may be DC but it will vary how do I calculate the ripple of Vout?

And how do I select a opamp for this type of application.What bandwidth should my opamp have?