AMIS-53000 Datasheet, PDF (16/99 Pages) AMI SEMICONDUCTOR – Frequency Agile Transceiver

AMIS-53000 Frequency Agile Transceiver
Data Sheet
5.0 Hardware Description
5.1 Frequency
The AMIS-53000 uses an internal VCO, PLL and trim capacitors with an external oscillator crystal to generate the RF frequencies for
both TX and RX. The external crystal is a parallel resonant mode crystal with required loading capacitors. The AMIS-53000 contains
internal load capacitors, typically sufficient for use with the suggested 24MHz. It is suggested that a 24MHz with 20ppm tolerance be
used with the AMIS-53000.
Figure 4: External Crystal Circuit
The internal VCO requires an external parallel LC to set the frequency for RX or TX. There is an internal capacitance that needs to be
considered when selecting the values of the inductor and capacitor. The AMIS-53000 is sensitive to the positioning of the LC
components in the layout of the PCB. The traces to the LC need to be as symmetrical as is possible. The location of the LC needs to
be as close to the AMIS-53000 pins as is practical. A simple layout change to these parameters can mean that the AMIS-53000 VCO
frequency will change causing a need to change the values of the inductor, capacitor and/or the values in the registers controlling the
RF frequency. The value of the inductor and/or the capacitor may need to be adjusted to allow the AMIS-53000 to calibrate the PLL for
a given frequency of operation. The layout of the printed circuit board for the inductor and capacitor should route traces connecting
other components away from the inductor and capacitor pads.
The VCO in the AMIS-53000 is a differential negative resistance oscillator (DNRO), commonly found in the literature. It uses an internal
voltage variable capacitor (varactor) in combination with an external L and C to provide the desired frequency. The output frequency is
found simply by:
Where: Ltot and Ctot are the total inductance and capacitance respectively at the VCO pins. This includes the internal capacitance of
approximately 2pF.
AMI Semiconductor – Aug. 05, Rev. 1.0
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