U2538B-MFP 데이터 시트보기 (PDF) - Atmel Corporation

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U2538B-MFP

IR Receiver for Data Communication

Atmel Corporation 

Functional Description

Input Stage (TIA)

Controlled Gain

Amplifier (CGA)

Bandpass Filter (BPF)

The input stage provides the necessary bias voltage for the photo diode and ensures

decoupling of the useful signal. This involves processing the DC and AC portions in sep-

arate parts of the circuit: the bias voltage (BIAS) and the transimpedance amplifier

circuit (TIA). The bias voltage circuit operates like a load resistor with respect to the

photo diode, the value of which is low for DC and low-frequency signals (3 to 100 kW),

but as high as possible for the operating frequency (100 kHz to 1 MHz) depending on

the input current). The ac portion of the input signal feeds an inverted amplifier with a

sufficiently low input resistance (Zi < 10 kW). If the input resistance is too high, the useful

signal will be lost due to the junction capacitance of the photodiode.

The controlled gain amplifier accounts for the greatest part of the voltage gain and can

be controlled via the voltage at CAGC (Pin 2). Gain control is needed to support the

interference suppression of the detector. High-pass behaviour results from the capaci-

tive coupling of the individual stages. The cut-off frequency is approximately 20 kHz.

The bandpass filter basically consists of integrated components. An external resistor

determines the mid-frequency. The filter quality is about 7 and is practically independent

of the selected mid-frequency (see Figure 3). The following formula can be used for cal-

culating the resistor, Rf0:

RfO(kW )

=

---8----8---5---5----- – 13

f0(kHz)

where: 20 kHz < f0 < 60 kHz

Figure 3. Characteristic of the Bandpass Filter

120

100

80

60

40

20

0

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

f/f0

4 U2538B

4717A–IRRC–05/03

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