ax5051 AXSEM, ax5051 Datasheet - Page 20

• Manufacturer Part Number: ax5051
• Description: Ax5051 Radio
• Manufacturer: AXSEM

20
Circuit Description
5.1.
The
internal circuitry at pin VREG from the primary supply VDD_IO. All VDD pins of the device must
be connected to VREG. The antenna pins ANTP and ANTN must be DC biased to VREG. The
I/O level of the digital pins is VDD_IO.
The voltage regulator requires a 1µF low ESR capacitor at pin VREG.
In power-down mode the voltage regulator typically outputs 1.7 V at VREG, if it is powered-
up its output rises to typically 2.5 V. At device power-up the regulator is in power-down
mode.
The voltage regulator must be powered-up before receive or transmit operations can be
initiated. This is handled automatically when programming the device modes via the
PWRMODE
Register
above 1.3 V or 2.3 V, sticky versions of the bits are provided that can be used to detect low
power events (brown-out detection).
5.2.
The on-chip crystal oscillator allows the use of an inexpensive quartz crystal as the RF
generation subsystem’s timing reference. Although a wider range of crystal frequencies can
be handled by the crystal oscillator circuit, it is recommended to use 16 MHz as reference
frequency since this choice allows all the typical SRD band RF frequencies to be generated.
The oscillator circuit is enabled by programming the
enabled.
To adjust the circuit’s characteristics to the quartz crystal being used without using additional
external components, both the transconductance and the tuning capacitance of the crystal
oscillator can be programmed.
The transconductance is programmed via register bits XTALOSCGM[3:0] in register XTALOSC.
The integrated programmable tuning capacitor bank makes it possible to connect the
oscillator directly to pins CLK16N and CLK16P without the need for external capacitors. It is
programmed using bits XTALCAP[5:0] in register XTALCAP.
To synchronize the receiver frequency to a carrier signal, the oscillator frequency could be
tuned using the capacitor bank however, the recommended method to implement
frequency synchronization is to make use of the high resolution RF frequency generation sub-
system together with the Automatic Frequency Control, both are described further down.
Alternatively a single ended reference (TXCO, CXO) may be used. The CMOS levels should
be applied to CLK16P via an AC coupling with the crystal oscillator enabled.
Version 1.6
AX5051
Voltage Regulator
Crystal Oscillator
VREG
register.
uses an on-chip voltage regulator to create a stable supply voltage for the
contains status bits that can be read to check if the regulated voltage is
PWRMODE
register. At power-up it is not
Datasheet AX5051