CLRC63201TSLASH0FE datasheet(141/163 Pages) PHILIPS

141 / 163 page

Philips Semiconductors

Product Specification Rev. 3.0; May 2003

Multiple Protocol Contactless Reader IC

CL RC632

141

Confidential

20.2.3 RECEIVING CIRCUIT

The internal receiving concept of the CL RC632 makes use of both side-bands of the sub-carrier load

modulation of the card response. No external filtering is required.

It is recommended to use the internally generated VMID potential as the input potential of pin RX. This DC

voltage level of VMID has to be coupled to the Rx-pin via R2. To provide a stable DC reference voltage a

capacitance C4 has to be connected between VMID and ground.

Considering the (AC) voltage limits at the Rx-pin the AC voltage divider of R1 + C3 and R2 has to be

designed. Depending on the antenna coil design and the impedance matching the voltage at the antenna coil

varies from antenna design to antenna design. Therefore the recommended way to design the receiving

circuit is to use the given values for R1, R2, and C3 from the above mentioned application note, and adjust

the voltage at the Rx-pin by varying R1 within the given limits.

Note: R2 is AC-wise connected to ground (via C4).

20.2.4 ANTENNA COIL

The precise calculation of the antenna coils’ inductance is not practicable but the inductance can be

estimated using the following formula. We recommend designing an antenna either with a circular or

rectangular shape.

LnH

l cm

[]

[] ln

=⋅

⋅











 −













l1............... Length of one turn of the conductor loop

D1 ............. Diameter of the wire or width of the PCB conductor respectively

K............... Antenna Shape Factor (K = 1,07 for circular antennas and K = 1,47 for square antennas)

N1 ............. Number of turns

ln .............. Natural logarithm function

The actual values of the antenna inductance, resistance, and capacitance at 13.56 MHz depend on

various parameters like:

•

antenna construction (Type of PCB)

•

thickness of conductor

•

distance between the windings

•

shielding layer

•

metal or ferrite in the near environment

Therefore a measurement of those parameters under real life conditions, or at least a rough measurement

and a tuning procedure is recommended to guarantee the optimum performance. For details refer to the

above mentioned application notes.

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