PCINT13 datasheet(194/294 Pages) ATMEL

194 / 294 page

194

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

16.3

Oscillator (Osc)

The frequency of the on-chip oscillator is controlled by a current fed into the RF input. An inte-

gr ate d com p e n s a tion c i r c uit en sur e s a wide te mp er atu r e ra ng e an d a

supply-voltage-independent frequency which is selected by a fixed resistor between RF (pin

15) and VS (pin 14). For 125kHz, a resistor value of 110k

Ω is defined. For other frequencies,

use the following formula:

This input can be used to adjust the frequency close to the resonance of the antenna.

Figure 16-5. Equivalent Circuit of the R

F Pin

16.4

Low-pass Filter (LPF)

The fully integrated low-pass filter (4th-order Butterworth) removes the remaining carrier sig-

nal and high-frequency disturbances after demodulation. The upper cut-off frequency of the

LPF depends on the selected oscillator frequency. The typical value is f

Osc/18. This means

data rates of up to f

Osc/25 are possible if biphase or Manchester signal encoding is used.

A high-pass characteristic results from the capacitive coupling at the input pin 4 as shown in

Figure 16-6. The input voltage swing is limited to 2V

pp. For frequency response calculation, the

impedances of the signal source and LPF input (typically 210k

Ω) have to be considered.

Figure 16-6. Equivalent Circuit of Pin Input

t[kΩ]

14375

0[kHz]

------------------

–

210k

10k

VBias + 0.4V

VBias - 0.4V

Input

PCINT13 Datasheet(PDF) 194 Page - ATMEL Corporation