SLRC400 Datasheet, PDF (110/130 Pages) NXP Semiconductors – I·CODE Reader IC

Philips Semiconductors
I•CODE Reader IC
Product Specification Rev. 2.0 November 2001
SL RC400
17.2 Circuit Description
17.2.1 EMC LOW PASS FILTER
The I•CODE system operates at a frequency of 13.56 MHz. This frequency is generated by a quartz
oscillator to clock the SL RC400 and is also the basis for driving the antenna with the 13.56 MHz carrier
frequenzy. This will not only cause emitted power at 13.56 MHz but will also emit power at higher harmonics.
The international EMC regulations define the amplitude of the emitted power in a broad frequency range.
Thus, an appropriate filtering of the output signal is necessary to fulfil these regulations.
A multi-layer board it is strongly recommended to implement a low pass filter as shown in the circuit above.
The low pass filter consists of the components L0 and C0. The values are given in table below.
Note: To achieve best performance all components shall have at least the quality of the recommended ones.
17.2.2 RECEIVING CIRCUIT
The internal receiving part of the SL RC400 uses a concept that benefits from both side-bands of the sub-
carrier load modulation of the label response. It is recommended to use the internally generated VMID
potential as the input potential of pin RX. To provide a stable reference voltage a capacitance C4 to ground
has to be connected to VMID. The receiving part of the reader needs a voltage divider connected between
the RX and the VMID pin. Additionally, it is recommended to use a series capacitance between the antenna
coil and the voltage divider. The circuit diagram above shows the recommended receiving circuit. The
receiving circuit consists of the components R1, R2, C3 and C4. The values are given in the table below.
Components
L0
C0
R1’
R1
R2
C3
Value
1 µH ± 5%
2 * 68 pF ± 2%
3.9 kΩ ± 1%
560 Ω ± 1%
820Ω ± 1%
1 nF ± 2%
Remark
Magnetic shielded e.g. TDK NL322522T-1R0J
NP0 material, Value depending on the antenna
inductance
NP0 material
Table 17-1: Values for the EMC- Filter and Receiving Circuit
Note: It is recommended not to use X7R material for the capacitors.
17.3 Calculation of the Antenna Coil Inductance
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.
L₁
[nH ]
=
2
⋅
l₁ [cm] ⋅




ln_
l₁
D₁


−
K



N₁₁^,
8
l₁.............. Length of the conductor loop of one turn
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
110
Preliminary