DEMO MANUAL DC112A DEMO MANUAL DC112A LT1328 IrDA Infrared Receiver U DESCRIPTIO This demonstration board implements the IrDA stan- Pin 3) in parallel with C4. The required filtering for V BIAS dards for infrared data communications. It is a complete (Pin 8) is provided by C6, a 1000pF cap to ground. The transmitter/receiver for use in SIR, FIR and 4PPM infrared DATA pin (Pin 5) is the output of the comparator. The data links. The LT 1328 is a photodiode receiver that quiescent, no signal state is a TTL HIGH a TTL LOW supports IrDA data rates up to 4Mbps, as well as other occurs when the photodiode receives light. Power re- modulation methods such as Sharp-ASK and TV remote quirements for the LT1328 are minimal: a single 5V control. This board can be configured for IrDA-SIR (Infra- supply and 2mA of quiescent current. The LT1328s ease red Data Association Serial Infrared), IrDA-FIR (Infrared of use and flexibility make it an ideal solution for numer- Data Association Fast Infrared) and 4PPM (4MHz pulse- ous other photodiode receiver applications. The LT1328 position modulation). is available in the 8-pin SO and the tiny MSOP package for size-critical applications. The LT1328, in the SO-8 and MSOP packages, contains all the necessary circuitry to convert current pulses from An IrDA transmitter is also provided on the demo board. an external photodiode to a digital TTL output, while Figure 2 shows the LED driver circuit and the LT1328 rejecting unwanted lower frequency interference. The receiver. The LED transmits light when the transmit input LT1328 requires only six external components to make pin on the demo board is high (5V), and is off when the an IrDA compatible receiver. Figure 1 is a block diagram Transmit Input is low (0V). The receiver output is the DATA of the LT1328. The preamp converts the photodiode pin on the demo board (which is Pin 5 on the LT1328). The current into a voltage that trips the comparator. The Data pin is high for no received light and a TTL LOW for a internal servo action suppresses only frequencies below light pulse. To switch from SIR to the faster data rates, a the R /C pole. This highpass filtering attenuates jumper is provided. Remote switching can be accom- gm FILT interfering signals, such as sunlight or incandescent and plished by removing the jumper and accessing the MODE fluorescent lamps, and is selectable at Pin 7 for low or pin: TTL HIGH for SIR and TTL LOW for faster data rates. high data rates. The upper frequency limit for the servo Actual transmit and receive waveforms can be seen in is set by an external capacitor C4. The pole is found by the Figures 3, 4 and 5 for SIR, FIR and 4PPM, respectively. formula f(Hz) = 25 1/(2 60k C4) a 330pF capacitor The lower waveform in each photo is the transmit input for C4 will pass signals above 200kHz (FIR and 4PPM). to the demo board. The upper waveform is the demo To lower the passband for SIR, move the jumper on the board DATA pin (Pin 5 of the LT1328). demo board from FIR, 4PPM to SIR. This takes the MODE , LTC and LT are registered trademarks of Linear Technology Corporation. pin (Pin 7) from ground to V , which switches C1 (on IrDA is a registered trademark of the Infrared Data Association. CC BOARD PHOTO 1DEMO MANUAL DC112A U W W PACKAGE AND SCHEMATIC DIAGRAMS V CC R FB 50k V 8 1.5V BIAS C6 1000pF 1 IN PREAMP BIAS D1 R IN PHOTODIODE 2k TEMIC BPV22NF MODE 7 HIGH: SIR LOW: FIR AND 4PPM FILTER DC SERVO + 2 FILTER g m 60k 5V C4 C1 V 6 CC 330pF 10nF 3 FILTER SWITCH + C2 C3 0.1F 10F 4 GND DATA 5 COMP DC112A BD Figure 1. LT1328 Block Diagram TOP VIEW IN 1 8 V BIAS TOP VIEW FILTER 2 7 MODE IN 1 8 V BIAS FILTER 3 6 FILTER 2 7 MODE V CC SWITCH FILTER SWITCH 3 6 V CC 4 5 GND DATA GND 4 5 DATA S8 PACKAGE MS8 PACKAGE 8-LEAD PLASTIC MSOP 8-LEAD PLASTIC SO LT1328CMS8 LT1328CS8 V CC JP1 U1 C6 D2 LT1328CS8 1000pF 12 3 HSDL-4220 1 8 IN SHDN R3 D1 V CC 6.3 2 7 BPV22NF E2 MODE R1 FILT MODE 1/2W 100 C1 3 6 FILTER V E3 V 5% CC CC 10nF SWITCH Q1 Q2 E6 TRANS 4 5 2N7002 2N7002 E4 DATA GND DATA R2 + C4 C2 C3 10k 330pF 0.1F 10F 5% E1 GND E5 GND DC112A TA01 DC112A TA02 Figure 2a. IrDA Receiver Figure 2b. IrDA Transmitter 2 + +