ANALOG DEVICES High Voltage Differential FET Amplifier FEATURES High Output Voltage: +140V High CMR: 100dB min Operates With a Wide Range of Power Supplies High CMV: (|Vs| - 10V) APPLICATIONS High Voltage Compliance Current Source High Voltage Follower With Gain High Voltage Integrator Diff. Amp for High CMV Bridge Applications Reference Power Supply GENERAL DESCRIPTION Model 171 is a high performance FET input op amp designed for operation over a wide range of supply voltages. This module features an output range of +15V to 140V at 10mA, a mini- mum CMRR of 100dB and a high common mode voltage rating of (Vs - 10V) min. DC offset is less than +1mV, and maximum drift of either 50 or 15uV/C is available in the J or K ver- sions. Bias current is less than 50pA (171J) or 20pA (171K), doubling per +10C increase of temperature. The model 171 also features small signal bandwidth of 3MHz for unity gain, full-power bandwidth of 15kHz, and slew rate of 10V/ps. These operating characteristics make model 171 an excellent choice for high voltage buffer applications, followers with gain, off-ground signal measurements and reference power supplies. Excellent power supply rejection of 74V/V enables model 171 to be powered by inexpensive, low regulation supplies, without sacrificing any of the 171s inherent high performance. The supplies also need not be symmetrical. Any combination of power supply voltages between the limits of 15 to +300V for the positive side and 15 to -300V for negative side is acceptable provided the total voltage across the amplifier is within the range of 30 to 300V. Model 171s output is completely short circuit protected by the use of a current limit scheme. This type of protection provides a short circuit output that is only slightly greater than the rated output current for normal operation. With this design the module and external circuitry are protected, internal heat dissi- pation and the associated high temperature rise are limited, and added reliability is built in. POWER SUPPLY VOLTAGES Model 171 offers the flexibility of operating with an extensive range and combination of power supply voltages. Figure 1 shows a chart of permissible combinations of supply voltages for the 171. The model 171 maintains its normal operating character- istics when using asymmetrical power supply configurations. POSITIVE SUPPLY VOLTAGE - Vg+ 0 +100V +200V +300V xX? y x 4 PERMISSIBLE COMBINATIONS ~ 7) OF SUPPLY VOLTAGES | Ae q & Ry ws ~ oe | yy v + Ss 100V P LL | = \ 7 SIGNAL RL Ve s yi Vg + 10V 5 Eg vg 10v | ~200V NEGATIVE SUPPLY VOLTAGE -Vg -300V | | | Figure 1. Power Supply Voltage Combinations OPERATIONAL AMPLIFIERS 77SPECIFICATIONS (typical @+25C and +125V unless otherwise noted) MODEL 171J 171K OUTLINE DIMENSIONS Dimensions shown in inches and (mm). OPEN LOOP GAIN 10 min * RATED OUTPUT pt 2.41 MAX {61.2} Voltage +(|Vo | -10V) min ots max Current +10mA min * (15.5) Maximum Load Capacitance 1000pF * ! uv UU FREQUENCY RESPONSE 0125 MAX (6.4) Unity Gain, Small Signal 3MHz * 0.20 MIN (5.1) Slewing Rate 10V/pts min * Full Power 15kHz min * EXT! Settling Time to 0.1%,+10V Step 25)4s * POT Overload Recovery SUS * * INPUT OFFSET VOLTAGE Initial Offset, +25C" +1mV * Avg. vs. Temp (0 to +70C) +50uV/C max +15pV/C max vs. Supply Voltage +7)4V/V * vs. Time 250uV/mo * BOTTOM VIEW 1. grip-| |. . (2.5) INPUT BIAS CURRENT Initial Bias, +25C -50pA max ~20pA max - NOTES: vs. Temp (0 to +70C) x 2/10C . 1. Pins: 0.040 *0.002 dia., spherical radius on ends, half-h Difference Current +19pA +5pA . -0.000 brass: gold plated. INPUT IMPEDANCE 2. Markings next to pins and grid are for reference only and Differential 10! QU3.5pF * do not appear on unit. Common Mode 10 QI 3.5 pF * * Available from Analog Devices #79PR1K INPUT NOISE Voltage, 0.01 to 1.0Hz 4uV p-p * 10Hz to 10kHz 2.uV rms * 5Hz to 50kHz 6uLV rms * MATING SOCKET Dimensions shown in inches and (mm). INPUT VOLTAGE RANGE Common Mode Voltage +( Vg |-10V) min * oo? MAX Common Mode Rejection 100dB min * pe oe re Common Mode Rejection 114dB * tT Toy TH oe 13270) Max Safe Differential Voltage tVe * gt rat pin au esx ean POWER SUPPLY __ 2%, a SIDE 82 t0 0.230 D/A Voltage, Rated Specification +25 to 150V dc * ! Apa os, Voltage, Operating +15 to +150V de * 031825 [EB] ewan ie + a Current, Quiescent +6mA - o te TEMPERATURE RANGE our | Rated Specification 0:0 +70C * 1750 *Vee Vee arospaces Operating -25C to 485C * too | ~ v =m l ON 0.300 (7.62} Storage -40C to +100C * (60.96) - |. | MECHANICAL - jot Case Size 2-41" x 1.82" x 0.61" 2] GPL] Etter sor Weight 80g * an D/A THRU (2 REQ'D) Mating Socket AC1037 * es (7-62) (18.24) *Specifications same as 171J * No external trim connection required. Specifications subject to change without notice. 78 OPERATIONAL AMPLIFIERS MATING SOCKET AC1037As shown in Figure 1, the model 171 requires at least +15 volts applied across it in order to operate properly. The 171 may be operated frorn a single floating supply voltage by using the power supply offsetting scheme shown in Figure 2. When this configuration is used, the 171 is capable of operating over its specified input and output voltage range. Vr +V5 + 3 OA\Ae Veo -15 + % IN ww > Vee > - 4 - Vs NVz= J -15V RL dO 15V Figure 2. Single Supply Operation FREQUENCY RESPONSE Figure 3 shows a plot of open loop gain and phase shift as a function of frequency for model 171. It can be seen that the model 171 is stable for all closed loop gains. At the crossover frequency, model 171 typically displays a phase margin of 85. 140 120 100 80 60 GAIN dB 40 PHASE SHIFT Degrees 20 Q 1 4 10 100 1k 10k FREQUENCY Hz 100k 1M Figure 3. Gain and Phase Shift vs. Frequency The open loop de gain of the model 171 does not change apprec- iably as the power supply voltage is varied (see Figure 4). Open loop gain is typically greater than 106dB over the full power supply voltage range. Figures 3 and 4 show that excellent closed loop accuracy is assured over a great range of frequency and supply voltage when using the 171. 140 120 100 80 60 GAIN dB 40 20 0 Qo 20 40 60 80 100 120 140 160 POWER SUPPLY VOLTAGE Volts Figure 4. Open Loop de Gain vs. Power Supply Voltage COMMON MODE REJECTION RATIO Common mode rejection is an important parameter in meas- urements requiring the amplification of small differential signals riding on high common-mode voltage levels. Model 171 is characterized by a minimum CMR of 100dB over its specified power supply voltage range. For the 171, CMR increases above this minimum value as the power supply voltage is raised. Figure 5 shows CMR as a function of supply voltage for model 171. The 171 also is capable of handling common-mode voltages up to 140 volts (with maximum supply voltages). 130 120 410 100 90 CMRR dB 80 70 60 0 25 50 75 100 125 150 75 POWER SUPPLY VOLTAGE -- Volts Figure 5. CMRR vs. Power Supply Voltage OFFSET VOLTAGE Model 171 provides excellent power supply rejection of 7WV/V and guaranteed input offset voltage drift of 154V/C (171K). The combination of these two characteristics, along with its gain and common mode performance, help make the model 171 an accurate and stable source of high voltage signals. Figure 6 shows input offset vs. power supply voltage for the 171. Supply rejection is fairly constant and is not dependent upon the power supply voltage level. 1200 1000 OFFSET VOLTAGE 0 20 40 60 80 100 120 140 160 POWER SUPPLY Volts Figure 6. Input Offset Voltage vs. Power Supply Voltage BIAS CURRENT The input bias current for the model 171 is specified to be SOpA, max for the J version and 20pA, max for the K version. These specifications are guaranteed over the normal range of common mode voltage. Bias current is a function of CMV and decreases as the CMV approaches zero volts. Figure 7 shows bias current vs. CMV for model 171K. Notice that with zero CMV the bias current is typically less than 3pA. 30 Vs = 4150V 20 to \ / +150 100 50 0 -50 COMMON MODE VOLTAGE Volts BIAS CURRENT pA -100 -150 Figure 7. Bias Current vs. CMV for Model 171K OPERATIONAL AMPLIFIERS 79APPLICATIONS There are rnany moderate-to-high voltage applications for which the model 171 FET-input op amp is useful. Typical classes of applications include: 1. Retrofit and auxiliary applications in existing analog com- puting systems utilizing a standard 100V signal-voltage range. 2. Use as low-noise buffers and input amplifiers in differential or non-inverting applications with signals derived from high- voltage sources. 3. Applications for which high output voltage is needed, e-g., wide-range precision reference sources. piezoelectric crystal drivers, etc. 4. Applications with moderate signal levels in systems subject to wide variation of supply voltage. Model 171s excellent performance characeristics, including high supply rejection, high input impedance, low noise, tolerance of capacitive load, and protection against output short circuits, make it ideal for all these classes of applicz tion. In addition, there is one more class that is a bit unusual. For an amplifier to be safe against short-circuits, it must not only be self-protected, it must also protect the supply that feeds it. The 171 is programmed to draw a maximum short-circuit current slightly greater than the 10mA maximum load current plus its quiescent current. Therefore, model 171 is the ideal choice for applications where a fail-safe current load that is essentially independent of supply voltage is needed. APPLICATIONS PROGRAMMABLE REFERENCE VOLTAGE SOURCE The operating specifications of the model 171 make it ideally suited for use as a low-cost, high voltage reference power supply. When coupled with an appropriate D/A converter, the 171 can also function as a 12 bit programmable voitage source. Such a network, utilizing Analog Devices DAC12.QZ converter, is shown in Figure 8. This system offers the versatility of binary or BCD coding and unipolar or bipolar output. Programmable levels of +50V or +100V are available by setting the output level on the D/A converter. The model 171 supply voliages can also be varied depending on the desired reference output levels. Gain control and offset contro! can be used, as shown in Figure 8. This type of reference supply network can be used in such applications as generation of calibration voltages (circuit or instrument testing) and low current control signal levels. Trim resistors are used in this circuit to precisely adjust the full scale and zero levels of the reference output. '10V OR _ '6V BIN = vet OR = pac BED 4 1202 Figure 8. Programmable Power Supply 80 OPERATIONAL AMPLIFIERS An expanded application for model 171 in a programmable voltage source for a mass spectrometer is shown in Figure 9. +200 TO +450V TO MASS. SPECTRO. METER PLATES. 12 BIT DIA --- COMMON GTO 1 10V] K. + 1 FIXED OFFSET Figure 9. Programmable Mass Spectrometer Voltage Source NONLINEAR CIRCUITS HANDBOOK in addition to its linear devices, Analog Devices also offers a comprchensive line of nonlinear function modules (multipliers, dividers, rms to dc converters, etc.). These function modules provide essential building blocks in systems that process infor- mation in industrial applications. In order to further the under- standing of function modules, Analog Devices has issued the Nonlinear Circuits Handbook. This handbook is an invaluable source of information on principles, circuitry, performance specifications, testing and application of the class of devices used in nonlinear applications. The handbook helps identify design situations for which nonlinear devices will offer the best solution and provides the fundamentals and guidelines necessary for the proper selection and use of function modules. The Non- linear Circuits Handbook is available from Analog Devices OTHER AMPLIFIERS @ High Performance FET model 52: low noise (1.5uV p-p, 1Hz BW), low drift (yV/C, 52K) low bias (3pA max), CMRR = 80dB min Wideband model 48: 15MHz (unity gain), low noise 2uV p-p, 1Hz BW, 300ns settling, 15uV/C drift (max) @ Wideband, Fast Settling - model 50: 70MHz (unity gain), 100mA output, 154V/C drift (max, 50K) Chopper Stabilized model 261: guaranteed low noise (1uV p-p max, 1Hz BW), +0.1pV/C drift (max, 261K) Economy Electrometer model 42: lowest bias (75 fA, 42K) e@ Higi Output Current model 50: 100mA output, wideband (10MHz, f,,), 80ns settling