Winceiver WE904/WE905
WiNEDGE & WiRELESS
0.1 - 1GHz Single Chip FM Transceiver
2003 WiNEDGE & WiRELESS PTE LTD
Page 15
Rev Date: 2003 May 27
FREQUENCY OF OPERATION
While the WE904/905 are well suited for use in the 902 to 928MHz ISM band, other frequencies
outside of this band are also applicable. The transmitter or receiver can be used with RF frequencies
from 100MHz to 1000MHz by suitable choice of external inductors or the receiver and transmitter
oscillator tank circuits.
Internal, programmable trim capacitors are provided for correction of any device tolerance.
Approximate center frequency calculations are given below:
Tx VCO
f = 1/{2 x SQRT[ (L+Lp) x Ct ] }
Rx VCO
f = 1/{2 x SQRT[ (L+Lp) x Cr ] }
[Note Rx VCO is 2x Rx local oscillator]
Where:
L is the external inductance connected to VDDT or VDDR, from both the true and inverted tank
outputs.
Lp (= 2.6nH) is the parasitic inductance for the TQFP or QFN 48 package.
Ct (= 4.6pF) is the total internal capacitance of TVCO, inclusive the TVCO varactor, internal trim
capacitance at middle trim value and parasitic capacitance for the TQFP and QFN-48 package.
Cr (= 1.7pF) is the total internal capacitance of RVCO, inclusive the RVCO varactor, internal trim
capacitance at middle trim value and parasitic capacitance for the TQFP and QFN-48 package.
The exact operating frequency is determined by programming of transmit and receive frequency
registers.
Assuming a ±5% tolerance on L, the guaranteed oscillator range is 3% of the center frequency if the
external inductor is set for devices from the center of the distribution. Devices at the edge of the
distribution can be brought to the correct center frequency by selection of the appropriate oscillator
trim bit.
The Tx trim is programmed by bits 21, 22 and 23 of the transmitter frequency register; the Rx trim is
programmed by bits 21 and 22 of the receiver frequency register.