Infineon BGT24LTR11 User Manual page 14

User's guide to BGT24LTR11
XENSIV™ 24 GHz radar MMIC
Table of contents
4 VCO control
4.1 VCO control using PTAT
Vctrl
R6
to VCC_PTAT
TX
TX_ON
Figure 18 Block diagram of using V_PTAT to keep BGT24LTR11 in the ISM band
BGT24LTR11 was designed to keep its transmit frequency inside the ISM band without the need for a dedicated
frequency control circuit like a PLL or an LUT based control of VTUNE. In Doppler radar mode, frequency
adjustment via V_PTAT is the most efficient way.
Exact frequency control in Doppler radars in the 24 GHz ISM band is not really necessary for most applications.
If we assume the transmit frequency to be at the lower edge of the band while it is actually at the upper edge,
the introduced error is only 0.8 %. However, it is necessary that the TX signal stays inside the ISM band under all
conditions.
The analog V control signal forces the VCO into the opposite direction in case of temperature drift. Doing so,
PTAT
the temperature effect of the VCO is strongly reduced. R1 adjusts the relative level of V
noise on V (V ), capacitor C5 (big capacitor) is charged by V
tune PTAT
save power during duty cycle OFF time. Going into duty cycle ON mode, the chip is fully supplied and VCC_PTAT
(via V ) is disconnected to drive VTUNE from C5.
ctrl
Application note
VCC
R5
C8
VCC
MPA
f-Div
VTUNE
IFI IFQ
BGT24LTR11
IFQ
90°
LNA
0°
IFI
R_TUNE
PTAT
V_PTAT
C5 R1
while the rest of the chip is turned OFF to
PTAT
14
RFIN
from Vctrl
. To buffer and reduce
PTAT
Revision 1.50
2023-02-14