Receiver for Optical Distance Measurement

Transcription

1 19-47; Rev ; 7/9 EVALUATION KIT AVAILABLE Receiver for Optical Distance Measurement General Description The is a high-gain linear preamplifier for distance measurement applications using a laser beam. The device operates from a single +5.V supply and converts current from an AC-coupled photodiode into a single-ended voltage signal. The input accepts single pulses or bursts of pulses with widths down to 3ns. The amplifier remains linear with input amplitudes from 42nA P (SNR = 3) to 4µA P. It can also withstand overload signals as large as 2mA P. The output stage is designed to drive a high-impedance load to deliver the output-voltage swing at the lowest possible power dissipation. The gain of the preamplifier stage is selected using the GA pin to be 6kΩ or 3kΩ. There is also an internal 14dB attenuator that is selected using the pin. The output stage can be disabled (high impedance). The device is available in a 3mm x 3mm, 12-pin TQFN package and operates over the -4 C to +5 C temperature range. Supply Voltage Linearity Range Up to 4µA P Overload Current Up to 2mA P Features 5mW Power Dissipation at +5.V 1.5pA/ Hz Noise Density at 6kΩ Gain 14nA RMS Input-Referred Noise at 6kΩ Gain Selectable Gains (6kΩ, 3kΩ) Selectable 14dB Attenuation PART Ordering Information TEMP RANGE P- PACKAGE +Denotes a lead(pb)-free/rohs-compliant package. *EP = Exposed pad. TOP MARK GTC+ -4 C to +5 C 12 TQFN-EP* ABN Applications LIDAR Sensors for Automotive Applications (ACC, Stop&Go) Laser Sensors for Portable Distance Measurement Laser Sensors for Industrial Applications Pin Configuration appears at end of data sheet. Typical Application Circuits TO +12V SGLE-CHANNEL RECEIVER P GA LEAR LIDAR Rx BUFF MAX1446 ADC * L AND C SET THE LOW-FREQUENCY CUTOFF REQUIRED FOR THE APPLICATION. Typical Application Circuits continued at end of data sheet. Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at , or visit Maxim s website at

2 ABSOLUTE MAXIMUM RATGS Supply Voltage Range, V to +6.V Voltage Range at,, GA V to ( +.5V) Current Range at,... -4mA to +4mA Continuous Power Dissipation (T A = +7 C) 12-Pin TQFN-EP (derate 16.7mW/ C above +7 C) mW Storage Temperature Range C to +15 C Lead Temperature (soldering, s)...+3 C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS ( = +4.5V to +5.5V, AC-coupled (C =.1µF) output load 2kΩ, T A = -4 C to +5 C. Typical values are at =, T A = +25 C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Power-Supply Current I CC (Note 2) 15 ma PUT SPECIFICATIONS Input-Referred Noise Input-Referred Noise Density Input Impedance CMOS/TTL PUT SPECIFICATIONS Output noise up to C = 5pF, GA = MHz/(gain at 5MHz) C = 5pF, GA = Output noise centered C = 5pF, GA = at 5MHz over Hz band/(gain at 5MHz) C = 5pF, GA = At 1MHz, GA = 1 8 At 1MHz, GA = 3 Input High Voltage V IH 2 V Input Low Voltage V IL.8 V Input Current Input Impedance GENERAL SPECIFICATIONS Small-Signal Transimpedance Small-Signal Bandwidth f 3dB C = 5pF I IH, I IL input ±15 I IH GA and inputs -18 R PULLUP input 6 R PULLDOWN GA and inputs 4 I 15μA P, GA = I 5μA P, GA = GA = 1, = GA =, = Gain Peaking 5pF C 15pF 1 db Attenuation Stability = 1; 2log(V ON /V OFF ) db PUT SPECIFICATIONS Total Harmonic Distortion Power-Supply Noise Rejection (Note 3) THD PSNR Frequency = 1MHz, GA = 1-54 V =.5V P GA = -53 Frequency = MHz, GA = 1-38 V =.5V P GA = -47 Noise frequency < 1MHz GA = 1-16 GA = -23 na RMS pa/ Hz μa k k MHz db db 2

3 ELECTRICAL CHARACTERISTICS (continued) ( = +4.5V to +5.5V, AC-coupled (C =.1µF) output load 2kΩ, T A = -4 C to +5 C. Typical values are at =, T A = +25 C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Attenuation in Disable Mode Output Impedance Frequency < 5MHz, = -71 2log(V _ABLED / V _ENABLED ) = 1-57 At 1MHz, =, =, GA = or 1 51 At 1MHz, =, = 1, GA = or At 1MHz, = 1, = or 1, GA = or 1 db 9 k Note 1: AC specifications are guaranteed by design and characterization. Note 2: Supply current is measured with unterminated or AC-coupled. Note 3: Measured by applying mv P-P sinusoidal noise to the supply voltage. PSNR is defined as 2log(V _NOISE /_NOISE ). Typical Operating Characteristics (Typical values are at =, T A = +25 C, C = 5pF, =, unless otherwise noted.) SUPPLY CURRENT (ma) SUPPLY CURRENT vs. TEMPERATURE = = 1 toc1 PUT VOLTAGE (VP) PUT VOLTAGE vs. PUT CURRENT GA = 1, = GA =, = GA = 1, = 1 GA =, = 1 toc2 TRANSIMPEDANCE (dbi) FREQUENCY RESPONSE GA = 1, = GA =, = GA = 1, = 1 GA =, = 1 toc TEMPERATURE (NC) PUT CURRENT (µa P ) FREQUENCY (MHz) 3

4 Typical Operating Characteristics (continued) (Typical values are at =, T A = +25 C, C = 5pF, =, unless otherwise noted.) BANDWIDTH (MHz) BANDWIDTH vs. PUT CAPACITANCE (GA = 1) T A = -4 NC T A = +25 NC T A = +5 NC = +5.V toc4 BANDWIDTH (MHz) BANDWIDTH vs. PUT CAPACITANCE (GA = 1) = +5.5V = +5.V = +4.5V toc5 GA PEAKG (db) GA = 1 GA PEAKG vs. PUT CAPACITANCE GA = toc6 BANDWIDTH (MHz) BANDWIDTH vs. PUT CAPACITANCE (GA = ) T A = -4NC T A = +5NC = toc7 BANDWIDTH (MHz) BANDWIDTH vs. PUT CAPACITANCE (GA = ) = +5.5V = +5.V = +4.5V toc8 PSNR (db) POWER-SUPPLY NOISE REJECTION (SUPPLY NOISE = mv P-P ) GA = 1, = 1 GA = 1, = GA =, = GA =, = 1 toc9-6 k k 1M M FREQUENCY (Hz) PUT-REFERRED NOISE (narms) PUT-REFERRED NOISE vs. PUT CAPACITANCE = GA = 1 BW = MHz T A = +5NC T A = -4NC toc PUT-REFERRED NOISE (narms) PUT-REFERRED NOISE vs. PUT CAPACITANCE GA = 1 BW = MHz = +5.5V = +5.V = +4.5V toc11 PUT-REFERRED NOISE (µvrms) PUT-REFERRED NOISE vs. PUT CAPACITANCE GA = 1 BW = MHz = +5.5V = +5.V = +4.5V toc

5 Typical Operating Characteristics (continued) (Typical values are at =, T A = +25 C, C = 5pF, =, unless otherwise noted.) PUT-REFERRED NOISE (narms) PUT-REFERRED NOISE vs. PUT CAPACITANCE = GA = BW = MHz T A = +5NC T A = -4NC toc13 PUT-REFERRED NOISE (narms) PUT-REFERRED NOISE vs. PUT CAPACITANCE GA = BW = MHz = +5.5V = +5.V = +4.5V toc14 PUT-REFERRED NOISE (µvrms) PUT-REFERRED NOISE vs. PUT CAPACITANCE GA = BW = MHz = +5.5V = +5.V = +4.5V toc TOTAL HARMONIC TORTION vs. FREQUENCY V =.5V P toc16 (5V/div) ABLE SWITCH (DC-BLOCK =.1µF, LOAD = 2kI) toc17-2 THD (db) -3 GA = 1 (2mV/div) -4 GA = FREQUENCY (MHz) ns/div GA SWITCH (DC-BLOCK =.1µF, LOAD = 2kI) toc18 SWITCH (DC-BLOCK =.1µF, LOAD = 2kI) toc19 GA (5V/div) (5V/div) (2mV/div) (5mV/div) 4µs/div 4µs/div 5

6 Typical Operating Characteristics (continued) (Typical values are at =, T A = +25 C, C = 5pF, =, unless otherwise noted.) TRANSIENT RESPONSE (LEAR REGION, GA = 1) toc2 TRANSIENT RESPONSE (OVERLOAD REGION, GA = 1) toc21 ZOOM TRANSIENT RESPONSE (OVERLOAD REGION, GA = 1) toc22 ZOOM 1µA P 2mA P 2mA P 6µs SETTLG TIME 6mV P 1.4V P 1.4V P 2MHz BW LIMIT 2MHz BW LIMIT.1µF DC-BLOCK 2kI LOAD 2ns/div ns/div µs/div Functional Diagram ENUATOR SWITCHABLE IMPEDANCE 6kΩ OR 3kΩ 6kΩ 4kΩ 4kΩ GA 6

7 P NAME FUNCTION 1, 12 5V Power-Supply Connection 2 Amplifier Input. Accepts AC-coupled photodiode input current. 3, 4 Supply Ground 5 Pin Description CMOS/TTL Input. Assert this pin high to enable a 14dB attenuator in the amplifier. Force this pin low to disable the attenuator. Contains internal 4k pulldown resistor. Connect to if not used. 6, 8, 11 N.C. Not Connected. This pin is not internally connected. 7 GA CMOS/TTL Input. Selects amplifier gain setting. Force high for 6k. Force low for 3k. Contains internal 4k pulldown resistor. 9 EP Amplifier Output. An increase in current into the pin causes the voltage at the pin to decrease. must be AC-coupled to a load of 2k or greater. CMOS/TTL Input. Force high to disable the output of the. Force low to enable the output. Contains internal 6k pullup resistor. Exposed Pad. The exposed pad must be soldered to circuit board ground for proper thermal and electrical performance. Detailed Description The preamplifier consists of a selectable-gain transimpedance amplifier, a selectable 14dB attenuator, and an output-driver block. The selectable-gain transimpedance amplifier linearly boosts the signal from the photodiode. This block is followed by an attenuator block that allows the user to attenuate the signal by 14dB selected by the pin. The final block is the output driver that can be disabled by asserting the pin. Transimpedance Amplifier The selectable-gain transimpedance amplifier is controlled by the GA pin. See Table 1 for gain settings. Attenuator The attenuator block can be set to pass the signal through to the output stage with db of attenuation ( forced low) or with 14dB of attenuation ( forced high). Output Driver The output driver is designed to drive an AC-coupled load with an impedance of 2kΩ or greater. The output can be disabled by asserting the pin high. When the output is disabled, the pin goes to a highimpedance state. See Figure 1 for the equivalent output circuit. WARNG: The output is designed to be AC-coupled to a high-impedance load. Operating the part with its output DC-coupled to through a 2kΩ or less load may damage the output. Applications Information Settling Time Settling time is the required time for the output to achieve the final steady-state or AC amplitude swing after a setting has been changed on the. The output common-mode voltage shifts when a change is Table 1. Transimpedance Gain Settings GA TRANSIMPEDANCE (k ) LEAR RANGE (μa P ) BANDWIDTH (MHz) 3 I I

8 2Ω 4Ω Ω Figure 1. Equivalent Output Circuit made to either the GA or setting. Table 2 provides typical output common-mode voltages for the combination of settings. Settling time is proportional to the RC time constant set by the output DC-blocking capacitor, load, and output impedance. For example, a.1µf DC-blocking capacitor, 2kΩ load, and 51Ω output impedance provide an RC time constant of approximately 2µs. After changing the GA or setting, the system should wait at least three to four time constants before analyzing received signals. Settling time is also required when changing the setting. When is asserted high, the output disables to high impedance and typically settles to steady state within 2ns. When is deasserted, the output enables and typically settles to steady state within 5ns. Overload Recovery Time Transistors saturate when the amplifier is overloaded, resulting in output distortion. Overload typically occurs with signals greater than 2µA P (GA = 1) or 4µA P (GA = ). It can withstand overload signals as large as 2mA P. Recovery time depends on the amplitude and duration of the overload pulse. Table 2. Output Common-Mode Voltages GA PUT COMMON-MODE VOLTAGE (V) Layout Considerations Noise performance and bandwidth are adversely affected by capacitance at the pad. Minimize capacitance on this pad and select a low-capacitance photodiode. Reducing PCB capacitance can be accomplished by removing the ground plane underneath the connection from the photodiode to the pin and by keeping the photodiode as close as possible to the. Use broadband power-supply filtering techniques to achieve the best sensitivity and noise performance. Exposed-Pad Package and Thermal Considerations The exposed pad on the 12-pin TQFN provides a very low thermal resistance path for heat removal from the IC. The pad is also electrical ground on the and must be soldered to the circuit board ground for proper thermal and electrical performance. Refer to Application Note 862: HFAN-8.1: Thermal Considerations of QFN and Other Exposed-Paddle Packages for additional information. TOP VIEW N.C. *EXPOSED PAD VCC 9 N.C. 8 GA 6 N.C *EP Pin Configuration 2 TH QFN (3mm 3mm) Package Information For the latest package outline information and land patterns, go to PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 12 TQFN-EP T

9 TO +12V P GA LEAR LIDAR Rx 7kΩ 3kΩ Typical Application Circuits (continued) MULTIPLE-CHANNEL RECEIVER TO +12V P GA LEAR LIDAR Rx 7kΩ 3kΩ MAX4311 4:1 MUX/AMP TO +12V BUFF MAX1446 ADC A A1 P GA LEAR LIDAR Rx 7kΩ 3kΩ 2 TO +12V 1 P GA LEAR LIDAR Rx 7kΩ 3kΩ 2 3 MICROCONTROLLER/DSP 3 * L AND C SET THE LOW-FREQUENCY CUTOFF REQUIRED FOR THE APPLICATION. Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.