Micore Reader IC Family; Directly Matched Antenna Design 

Basic parameter design for 106kbit/s

A complete Micore reader antenna design can be done in steps based on the certain number of given parameters given below. E very step is described in one of the following sections . The best way to design antenna is to follow the steps given below:

  1. Design a coil, measure L and R or L and Q.
  2. Calculate the resonance capacitors to design a resonance circuitry together with the coil.
  3. Tune this resonance circuitry to the required impedance.
  4. Connect the resonance circuitry to the EMC low pass filter output, check the ITVDD and if necessary retune the components for optimum performance.
  5. Check & adjust the Q-factor.
  6. Check & adjust the receive circuitry .

Remark: This design might not be completely compliant to the ISO/IEC 14443 (with higher bit rates) due to some simplification in the design steps. For an ISO/IEC 14443 compliant design the complete design steps need to be taken into account 

 Given parameters

Mifare 4K Proximity Contactless Cards,NXP Mifare 4k Offset Printing Cards,Mifare Classic 4K Card.

Fig 3. Given design values for basic parameter antenna design: EMC-filter and matching

To reduce the number of parameters for the basic parameter antenna design, the following fixed component values shall be used:
Table 2: Fixed value of components of directly matched antenna
Component Value
C3 1nF (Ceramic NP0, tolerance ≤ ±10%)
C4 100nF (Ceramic X7R, tolerance ≤ ±10%)
R1 470Ω .. 4.7kΩ 2
R1 820Ω

Remark: GND should be one GND-plane for the Micore circuitry itself, and should be directly connected to the center pin of the shielding, if shielding is applicable. It is not required to connect the center tapping of the antenna coil.

HF 13.56MHz Mifare 4K Cards ,NXP Mifare 4k Pre-printed cards,NXP Mifare 4K Printed Cards,NXP Mifare 4k Offset Printing Cards

Fig 4. Antenna circuitry
The complete directly matched antenna consists of the parts as shown in Fig 4

Table 3: Components of antenna circuitry
Component Value
LCoil Antenna coil
Rcoil Internal resistor of the antenna coil
RSa,RSb External resistor
C1a, C1b, C2a, C2b Capacitors to match impedance and resonance

 

The antenna coil

As a start the required antenna coil shall be designed within the mechanical application requirements and according to the general antenna design rules.

The inductance L = L + L and series resistor R = 2⋅ R shall be measured

a b L coil

between A and B in this measurement could be done with an impedance analyzer or an LCR meter at a frequency of f = 13.56 MHz.

 Fig 5. Antenna coil circuitry and relation between radius and number of turnsHF 13.56MHz Proximity Cards,Mifare 4K Card,NXP Mifare 4k Offset Printing Cards,Mifare 4k Printing Cards.

Depending on the antenna radius use either a single turn coil (r ≥ 5 cm) or a double turn coil (r < 5 cm) for each coil La and Lb.

The antenna coil shall be symmetrical.

The (electrical) center point can be connected to GND. If this center point is connected to GND, it is suggested to use the same number of complete turns for both La and Lb (even number of turns for L), to keep this center point as near as possible to the antenna coil connector. If one and a half turns are used, no center tapping shall be used. The shielding (if applicable) shall be connected to GND directly at the antenna connector (center tapped). Two layout examples based on a 2-layer board are shown in Fig 6.

Mifare 4K Proximity Cards,HF 13.56MHz Mifare 4K Cards,Mifare 4k Printing Cards,NXP Mifare 4K Printed Cards.

(1) Top layer (black) and Bottom layer (brown)
Fig 6. Example antenna coil layout with connected center tapping

According to the given design rules (coil radius ≈ operating distance, and number of turns as shown in Fig 5 ) the ind uctance of the antenna coil usually is between

L = La + Lb = 300nH…2µH R = 2⋅ R = 0.5Ω…5Ω

L coil

Remark: These values are only typical values.

The turn direction of the two parts of the coil (La and Lb) should be considered!

The antenna shall be measured completely (La + Lb between A and B) because of the coupling between the two parts of the antenna coil (La and Lb).

The measured value of RL is usually too high due to the high Q-factor of the coil. This has to be considered as follows. The effect is really low, as on one hand the influence of a slight change of RL on the matching is not high, and on the other hand the Q-factor has to be checked later anyway.

To be measured at 13.56 MHz.

It is not required to connect the center tapping of the coil, but it is required to connect the shielding (if applicable) to GND.