4

LT1319

FREQUENCY (Hz)

100k

1M

10M

100M

1319 G01

5

4

3

2

1

0

–1

–2

–3

–4

–5

50pF

30pF

10pF

Preamp Frequency Response vs

Input Capacitance

HIGHPASS CORNER FREQUENCY (Hz)

1k

100k

10k

1M

10M

1319 G03

1000

100

10

1

HIGHPASS CORNER FREQUENCY (Hz)

100

10k

100k

1M

1319 G02

1k

1000

100

10

1

0.1

Preamp Highpass vs

Capacitance on FILT1

Gain Stage Highpass vs

Capacitance on FILT2 or FILT2L

Preamp Output Noise vs

Input Capacitance

Input-Referred Noise vs

Lowpass Filter on PREOUT

FILTIN- or FILTINL- Referred

20

1.0

0.9

0.8

0.7

0.6

0.5

1319 G06

30

40

CIRCUIT DESCRIPTIO

The LT1319 is a general purpose low noise, high speed,

high gain, infrared receiver designed to easily provide IR

communications with portable computers, PDAs, desktop

computers and peripherals. The receiver takes the photo-

current from an infrared photodiode (Siemens BPW34FA

or Temic BPV22NF) and performs a current-to-voltage

conversion. After external filtering that is tailored for the

desired communication standard, two filter buffers are

provided. There are dual gain chains with nominal gain of

400V/V that feed internal comparators with hysteresis. The

comparator thresholds are set externally with a current into

time of 25ns and is well-suited to high data rates.

The low frequency comparator responds in 60ns and is

useful for more modest data rates such as Sharp/Newton

and IRDA-SIR. The circuit also contains shutdown circuitry

to reduce power consumption. Rejection of ambient inter-

ference is accomplished with AC coupling loops around the

preamp and the two gain stages. The rejection frequency is

set with an internal resistor and an external capacitor to

ground. This feature allows changing of the break fre-

quency by simply switching in additional capacitors. To aid

in rejection of power supply noise there is internal supply

regulation and a fully differential topology after the filter

buffers.

FREQUENCY (Hz)

250

200

150

100

50

0

10k

1M

10M

100M

1319 G04

100k

10pF

30pF

50pF

FILTER CUTOFF FREQUENCY (MHz)

0.1

20

15

10

5

0

110

1319 G05