DEMO MANUAL DC1416 LT1222 and LT1793 Low Noise Transimpedance Amplifier DESCRIPTION Demonstration circuit 1416 is a low noise transimpedance amplifier. It utilizes the low voltage noise LT(R)1222 op amp, and the low current noise LT1793 op amp, along with the discrete NXP JFET BF8621 or equivalent, allowing the user to take advantage of each component's particular opti- mization. These components are arranged with jumpers allowing various composite configurations. A socketed photodiode, OSRAM SFH213, is also provided. Design files for this circuit board are available at http://www.linear.com/demo/DC1416 All registered trademarks and trademarks are the property of their respective owners. PERFORMANCE SUMMARY Specifications are at TA = 25C, VS = 12V SYMBOL PARAMETER CONDITIONS VS Supply Voltage AZ TIA Gain VOS Input Offset Voltage TYP UNITS 12 V 1M LT1793 (VOS + IBIAS * 10M) 300 V dVOS /dT Input Offset Voltage Drift LT1793 (dVOS/dT +dIBIAS/dT * 10M) 10 V/C IBIAS Input Bias Current LT1793 + BF8621 6 pA en Input Voltage Noise Density f = 100kHz, JFET In Gain Configuration 1 nV/Hz en Input Voltage Noise Density f = 100kHz, Source Follower Configuration 3 nV/Hz CIN Input Capacitance f = 10kHz, Source Follower Configuration 2 pF GBW Gain Bandwidth Product JP In (CCOMP = 49pF) 70 MHz GBW Gain Bandwidth Product JP Out (CCOMP = 10pF) 190 MHz GBW Gain Bandwidth Product JP Out, C7 Removed (CCOMP = 0pF) 500 MHz 2 MHz BW -3dB Bandwidth With SFH213, 1M Gain, JP7 Out VOUT Output Voltage Swing Cathode Input, Integrator In 0 to 10 V VOUT Output Voltage Swing Cathode Input, Integrator Out -0.4 to -10 V VOUT Output Voltage Swing Anode Input, Integrator In 0 to -10 V VOUT Output Voltage Swing Anode Input, Integrator Out -0.4 to -10 V ICC Supply Current VS = 12V 17 mA IBIAS Input Bias Current LT1793 + BF8621 6 pA PSRR Power Supply Rejection Ratio 5V to 15V, Integrator In 95 dB Note 1) BF862 has been obsoleted as of 2017. On-Semi 2SK932-22 has been substituted, with practically identical performance. dc1416fa 1 DEMO MANUAL DC1416 OPERATING PRINCIPLES Composite amplifiers using single JFET inputs can be classified into two groups: common drain (or "source follower") and common source (or "JFET in gain"). The standard jumper configuration of this board, as shipped and as indicated on the silkscreen, has the JFET as a source follower. Another classification is DC accuracy. The LT1793 has been provided on board as an integrator to provide DC accuracy, overriding the high 400mV or so VGS of the JFET. The standard jumper configuration is "Integrator In", so the TIA will be DC accurate to within the VOS of the LT1793 (900V max). With the integrator removed from the circuit, the DC error rises to 400mV or so. The feedback resistor, which sets the TIA gain, is 1M. So the output will respond at 1V per microamp of photocurrent. QUICK START PROCEDURE Demonstration circuit 1416 is shipped with the jumpers set for source follower operation with the integrator in. If the jumpers have been changed, restore them to the positions shown in the schematic. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. With power off, connect the +12V, -12V, and Com leads from the power supply to the V+, V-, and GND terminals of the demo circuit, as shown in Figure 1. 2. With power off, connect the VOUT of the demo circuit to an oscilloscope or DMM. You can use either the gold SMA connector or the turrets provided on board, or both. Set a high range such as 2V/DIV on the oscilloscope, or VDC on the DMM. 3. Turn on the power supply. 2 4. You should now be able to wave your hand over the clear photodiode provided on the board (upper left of Figure 1) and see the effect in both DC signal and noise. With the photodiode in darkness, or removed from its socket, the output should sit near ground. 5. You can now connect an optical source to excite the photodiode in a more controlled manner. The easiest way is to drive an LED directly from a function generator, with the function generator's internal 50 source impedance as a current limiter. Any standard color or IR LED can be used, as the photodiode provided has a wide sensitivity. Be careful not to overdrive sensitive devices such as small lasers. 6. You can now decide whether to play with other configurations (JFET in gain, integrator out, more compensation, etc), or to replace the provided photodiode with the one you intend to use. dc1416fa DEMO MANUAL DC1416 QUICK START PROCEDURE DC1416 F01 12 - + 12 POWER SUPPLY - + Figure 1. Proper Supply Connections. Board Is Shown for Source Follower with Integrator In (JP1 through JP6 Have Shunt in Position 1. JP7 and JP8 Are Open.) Table 1. Jumper Settings for Various Configurations. Refer to Figures 2 and 3 for Qualitative Descriptions of the Configurations and to Figure 4 for the Complete Schematic. JUMPER TYPE CIRCUIT SOURCE FOLLOWER INTEGRATOR IN SOURCE FOLLOWER INTEGRATOR OUT JFET IN GAIN INTEGRATOR IN JFET IN GAIN INTEGRATOR OUT JP1 1x3 JFET Drain 1, 2 1, 2 2, 3 2, 3 JP2 2x3 JFET Source 1, 2 1, 2 5, 6 3, 4 JP3 1x3 LT1222 -Input 1, 2 1, 2 2, 3 2, 3 JP4 1x3 Photodiode Bias 1, 2 1, 2 1, 2 1, 2 JP5 1x3 Integrator Output 1, 2 Out 2, 3 Out JP6 1x3 Integrator Input 1, 2 2, 3 1, 2 2, 3 JP7 1x2 LT1222 Compensation Out Out In In JP8 1x2 LT1222 +Input Out In Out Out dc1416fa 3 DEMO MANUAL DC1416 +12V G +12V R1 1M D S NXP BF862 R7 3.01k -12V R3 2.49k - + R1 1M LT1222 G VOUT -12V D + NXP BF862 S 2V - VOUT LT1222 DC1416 F02 -12V SOURCE FOLLOWER JFET IN GAIN Figure 2. The Two Basic Types of JFET Configuration. The Left Shows the JFET as a Source Follower, Simply Buffering the Feedback Resistor to the Op Amp's Inverting Input. The Right Shows the JFET In Gain, with Source Grounded. Because the JFET Inverts, the Feedback Is Now Applied to the Op Amp's Non-Inverting Input. In Both Cases, the Effective Input Offset Voltage Is One JFET VGS (About -400mV). The Source Follower Configuration Is the Simplest and Most Versatile, but the JFET In Gain Configuration Offers the Highest Achievable Gain-Bandwidth Product and the Lowest Voltage Noise. Output Noise at Low and Medium Frequencies (10kHz to 100kHz) Is 130nV/Hz, Dominated Entirely by the Feedback Resistor +12V G +12V R1 1M D S NXP BF862 R7 3.01k -12V R3 2.49k - + LT1222 -12V G VOUT D + NXP BF862 S 2V - - + LT1793 SOURCE FOLLOWER WITH INTEGRATOR R10 1k C9 10nF R6 221 R11 10M VOUT LT1222 -12V C9 10nF R11 10M R1 1M - + LT1793 DC1416 F03 JFET IN GAIN WITH INTEGRATOR Figure 3. The Two Basic Types of JFET Configuration Again, but Shown with LT1793 Integrators which Zero Out the Overall Input Offset Voltage. On the Left, the JFET VGS Is Forced to the LT1793 Non-Inverting Input. On the Right, the Integrator Puts JFET VGS at the Source Directly. In both Cases, the 10M Sensing Resistor R11 Injects 40fA/Hz of Current Noise, which Is Discernible but Relatively Small Compared to the 130fA/Hz of the 1M Feedback Resistor. The Output Noise at Low to Medium Frequencies Is about 136nV/Hz 4 dc1416fa A B C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. 5 4 JP7 3 2 GLEN B. 2 JP6 Figure 4. DC1416 Demo Circuit Schematic JP8 3 1 TECHNOLOGY J1 1 D 4 5 A B C D DEMO MANUAL DC1416 SCHEMATIC DIAGRAM dc1416fa 5 DEMO MANUAL DC1416 ESD Caution ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality. Legal Terms and Conditions By using the evaluation board discussed herein (together with any tools, components documentation or support materials, the "Evaluation Board"), you are agreeing to be bound by the terms and conditions set forth below ("Agreement") unless you have purchased the Evaluation Board, in which case the Analog Devices Standard Terms and Conditions of Sale shall govern. Do not use the Evaluation Board until you have read and agreed to the Agreement. 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