How can I convert a oscillator waveform (0.4 v amplitude ,500hz)shown in the pictures into pulse or square waveform. kindly suggest me any cmos ckt that can be run in 0.4 V supply voltage for this conversion.
You can easily use a comparator Like LM293 , LM339, LM319, ... etc. These comparators have open collector output, just a pull-up resistor to your desired voltage like 15V, 5V or 3.3V.
You can compare the voltage with 0V (GND) or if you want you can use 2 comparators as a window detector (for Example +0.1 , -0.1V). Check their Datasheet for Many Interesting Circuits.
your Power Supply voltage is 0.4V or Your input has 0.4V amplitude?
if your input voltage has 0.4V amplitude, there will no problem using comparators like LM319, ...etc
BUT if your power supply voltage is 0.4V , simply i don't know! it seems to me that this is some part of IC design and i think you should ask your question in IC Design Section.