>>>>> Exactly. But to get the same speed, meaning same signal
>>>>> impedence, you would need 1.2Kohms since
>>>>> 2Kohm // 3Kohm =3D 1.2Kohm.
>>>> On rising edge I don't see how does mentioned in your calcs
>>>> 3Kohm divider's bottom resistor help to speed the rising.
>>> This is very basic electronics. =A0Look up something called
>>> "Thevenin Equivalent".
>>
>> Interesting, obviously, removing the bottom resistor from the divider
>> would increase the speed of rising (assuming inputs would tolerate
>> it). But, according to your logic/formula removing the bottom resistor
>> would increase impedance and, thus, decrease the speed of rising.
>
> Not exactly. With two resistors the impedance is 1.2k and with only one
> it's 2k. But the equivalent voltages are 3.3 and 5 respectively. If you
> are driving logic with TTL(1.2 volt) thresholds the rise times will be
> very close.

TI CC1101 is not TTL.
>From its datasheet:
4.8 DC Characteristics
Logic "1" input voltage (VDD-0.7V) to VDD

For your 3.3V it will be >=3D2.6V.
Obviously the presence of the bottom resistor of the divider would
slow the signal rising to that level, the times with/without the
resistor should not be "very close".

-- =

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