Need help with CMOS 7555 abstable output @ 800 KHz please

[Marcus2012]

Hello

I'm new to the forum and I was looking for some help regarding an astable output I am trying to obtain from CMOS 7555 timer if possible please. I'm simulating a basic Modified Sine Wave generator for a high frequency wave using Circuit Wizard. I've created the circuit and it seems to work ok in simulations however the output from the 7555 is not a square wave but rather triangular in the simulation. The IC is rated for 1 MHz as I understand it so It should be ok and is this just a result of the slew rate of the timer? The J-k Flip-flops still seem to recognise the negative edge without a problem in the simulation I am just wondering if this is to be expected and will still function as an astable output in reality. I have attached the circuit diagram for the 7555 component and also the simulation output, red wave is the 7555 output and the blue wave is the produced modified sine wave. I would appreciate any help anyone could provide please.

Thanks

Values
C1 - 0.00001 µF
R1 - 15 KΩ
R2 - 82 KΩ
Frequency - 806145.2514 Hz.
Duty Cycle - 54.2 %

[Pauldf]

You may get a more square waveform if you use the output to drive a darlington pair transistor such as a TIP110

[Richard]

I expect that it is asking a bit too much to expect a perfect near-1MHz square wave at the output of the chip because the output flip flop may not have a good enough slew rate. I suggest that you put a high speed comparator at the output of the 7555, (loads available on the net) and take care with layout and decoupling when you make the circuit up.