Texas Instruments CC400DK, Руководство пользователя, Страница: 5 / 22

CC400DK Development kit (rev. 1.5) 2002-09-17 Page 5 of 22
Figure: The power connector with an amperemeter attached.
RF-section
The RF section consists of a CC400 chip with external components. The different
components are explained below.
The loop filter
The PLL loop filter contains the components C121-C123 and R121-R123. The software
program calculates the component values. Using the calculated component values for the
loop filter will give an optimum loop bandwidth for the selected system parameters.
The component values used in the CC400EB is selected for 9.6 kbit/s data rate, but can also
be used for evaluation of lower data rates.
The transmitted frequency is FSK modulated, which means that the bits ‘0’ and ‘1’ has
different frequencies, see Frequency separation in chapter 4.1.1.5 in SmartRF
®
Studio user
manual.
Note: If you need a shorter switching time between the two frequencies, the PLL settling time
has to be shorter. To find the new component values that you need for the loop filter, the
software program can be used as a calculator. Using a higher data rate value will give you a
larger loop bandwidth, but also an increase in the side-band noise on the carrier. A warning
may appear when increasing the data rate. To get around this warning, try to set the X-tal
accuracy to zero. Do not update the device when doing this, but use Enter to calculate the
values and return to your earlier settings afterwards.
External IF filter
The evaluation board is equipped with an external 455kHz ceramic filter. Input and output
impedance to the CC400 is 1.5k
Ω
, and the bandwidth is approximately 30kHz.
4-10V
0V
3V
I
out
A