PRODUCT SPECIFICATION
nRF2401A Single Chip 2.4 GHz Radio Transceiver
Nordic Semiconductor ASA - Vestre Rosten 81, N-7075 Tiller, Norway - Phone +4772898900 - Fax +4772898989
Revision: 1.1 Page 33 of 40 March 2006
Sharing crystal with micro controller.
When using a micro controller to drive the crystal reference input XC1 of the
nRF2401A transceiver some rules must be followed.
Crystal parameters:
When the micro controller drives the nRF2401A clock input, the requirement of load
capacitance C
L
is set by the micro controller only. The frequency accuracy of 30 ppm
is still required to get a functional radio link. The nRF2401A will load the crystal by
0.5pF at XC1 in addition to the PBC routing.
Input crystal amplitude & Current consumption
The input signal should not have amplitudes exceeding any rail voltage, but any DC-
voltage within this is OK. Exceeding rail voltage will excite the ESD structure and the
radio performance is degraded below specification. If testing the nRF2401A with a
RF source with no DC offset as the reference source, the input signal will go below
the ground level, which is not acceptable.
XC1
XO_OUT
Amplitude
controlled
current source
Buffer:
Sine to
full swing
Current starved
inverter:
XOSC core
XC2
Vdd
Vss
Vdd
Vss
ESD
ESD
Figure 19 Principle of crystal oscillator
It is recommended to use a DC-block before the XC1 pin so that the internal ESD
structures will self bias the XC1 voltage.
The nRF2401A crystal oscillator is amplitude regulated. To achieve low current
consumption and also good signal-to-noise ratio, it is recommended to use an input
signal larger than 0.4 V-peak. The needed input swing is independent of the crystal
