LMV716MM

LMV716 5 MHz, Low Noise, RRO, Dual Operational Amplifier with CMOS Input September 2006 LMV716 5 MHz, Low Noise, RRO, Dual Operational Amplifier with CMOS Input General Description The LMV716 is a dual operational amplifier with both low supply voltage and low supply current, making it ideal for portable applications. The LMV716 CMOS input stage drives the IBIAS current down to 0.6 pA; this coupled with the low makes the LMV716 perfect noise voltage of 12.8 nV/ for applications requiring active filters, transimpedance amplifiers, and HDD vibration cancellation circuitry. Along with great noise sensitivity, small signal applications will benefit from the large gain bandwidth of 5 MHz coupled with the minimal supply current of 1.6 mA and a slew rate of 5.8 V/µs. The LMV716 provides rail-to-rail output swing into heavy loads. The input common-mode voltage range includes ground, which is ideal for ground sensing applications. The LMV716 has a supply voltage spanning 2.7V to 5V and is offered in an 8-pin MSOP package that functions across the wide temperature range of −40˚C to 85˚C. This small package makes it possible to place the LMV716 next to sensors, thus reducing external noise pickup. Features (Typical values, V+ = 3.3V, TA = 25˚C, unless otherwise specified) n Input noise voltage 12.8 nV/ n Input bias current 0.6 pA n Offset voltage 1.6 mV n CMRR 80 dB n Open loop gain 122 dB n Rail-to-rail output n GBW 5 MHz n Slew rate 5.8 V/µs n Supply current 1.6 mA n Supply voltage range 2.7V to 5V n Operating temperature −40˚C to 85˚C n 8-pin MSOP package Applications n n n n Active filters Transimpedance amplifiers Audio preamp HDD vibration cancellation circuitry Typical Application Circuit 20179539 High Gain Band Pass Filter © 2006 National Semiconductor Corporation DS201795 www.national.com LMV716 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Tolerance (Note 2) Human Body Model Machine Model Supply Voltage (V – V ) Storage Temperature Range Junction Temperature (Note 3) + − Mounting Temperature Infrared or Convection (20 sec) 260˚C Operating Ratings (Note 1) Supply Voltage Temperature Range Thermal Resistance (θJA) 8-Pin MSOP 195˚C/W 2.7V to 5V −40˚C to 85˚C 2000V 200V 5.5V −65˚C to 150˚C 150˚C max 3.3V Electrical Characteristics (Note 4) Unless otherwise specified, all limits are guaranteed for TJ = 25˚C, V+ = 3.3V, V− = 0V. VCM = V+/2. Boldface limits apply at the temperature extremes (Note 5). Symbol VOS IB IOS CMRR PSRR CMVR AVOL Parameter Input Offset Voltage Input Bias Current Input Offset Current Common Mode Rejection Ratio Power Supply Rejection Ratio Common Mode Voltage Range Open Loop Voltage Gain 0 ≤ VCM ≤ 2.1V 2.7V ≤ V+ ≤ 5V, VCM = 1V For CMRR ≥ 50 dB Sourcing RL = 10 kΩ to V+/2, VO = 1.65V to 2.9V Sinking RL = 10 kΩ to V+/2, VO = 0.4V to 1.65V Sourcing RL = 600Ω to V+/2, VO = 1.65V to 2.8V Sinking RL = 600Ω to V+/2, VO = 0.5V to 1.65V VO Output Swing High RL = 10 kΩ to V+/2 RL = 600Ω to V+/2 Output Swing Low RL = 10 kΩ to V+/2 RL = 600Ω to V+/2 IOUT Output Current Sourcing, VO = 0V Sinking, VO = 3.3V IS SR GBW Supply Current Slew Rate Gain Bandwidth VCM = 1V (Note 9) 20 15 30 25 60 50 70 60 −0.2 80 76 80 76 80 76 80 76 3.22 3.17 3.12 3.07 122 Condition VCM = 1V (Note 8) Min (Note 6) Typ (Note 7) 1.6 0.6 1 80 82 2.2 Max (Note 6) 5 6 115 130 Units mV pA pA dB dB V 122 105 dB 112 3.29 3.22 0.03 0.07 31 41 1.6 5.8 5 2.0 3 mA 0.12 0.16 0.23 0.27 V mA V/µs MHz www.national.com 2 LMV716 3.3V Electrical Characteristics (Note 4) Unless otherwise specified, all limits are guaranteed for TJ = 25˚C, V+ = 3.3V, V− = 0V. VCM = V+/2. Boldface limits apply at the temperature extremes (Note 5). (Continued) Symbol en in Parameter Input-Referred Voltage Noise Input-Referred Current Noise Condition f = 1 kHz f = 1 kHz Min (Note 6) Typ (Note 7) 12.8 0.01 Max (Note 6) Units nV/ pA/ Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics. Note 2: Human Body Model is 1.5 kΩ in series with 100 pF. Machine Model is 0Ω in series with 100 pF. Note 3: The maximum power dissipation is a function of TJ(MAX), θJA and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX)-TA)/θJA. All numbers apply for packages soldered directly into a PC board. Note 4: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factor testing conditions result in very limited self-heating of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the device maybe permanently degraded, either mechanically or electrically. Note 5: Boldface limits apply to temperature range of −40˚C to 85˚C. Note 6: All limits are guaranteed by testing or statistical analysis. Note 7: Typical values represent the most likely parametric norm. Note 8: Input bias current is guaranteed by design. Note 9: Number specified is the lower of the positive and negative slew rates. Connection Diagram 8-Pin MSOP 20179540 Top View Ordering Information Package 8-Pin MSOP Part Number LMV716MM LMV716MMX Package Marking AR3A Transport Media 1k Units Tape and Reel 3.5k Units Tape and Reel NSC Drawing MUA08A 3 www.national.com LMV716 Simplified Schematic 20179529 www.national.com 4 LMV716 Typical Performance Characteristics Supply Current vs. Supply Voltage Unless otherwise specified, V+ 3.3V, TJ = 25˚C. Offset Voltage vs. Common Mode 20179506 20179505 Input Bias Current vs. Common Mode Input Bias Current vs. Common Mode 20179527 20179526 Input Bias Current vs. Common Mode Output Positive Swing vs. Supply Voltage 20179525 20179585 5 www.national.com LMV716 Typical Performance Characteristics Unless otherwise specified, V+ 3.3V, TJ = 25˚C. Output Negative Swing vs. Supply Voltage (Continued) Output Positive Swing vs. Supply Voltage 20179502 20179501 Output Negative Swing vs. Supply Voltage Sinking Current vs. VOUT 20179584 20179503 Sourcing Current vs. VOUT PSRR vs. Frequency 20179504 20179531 www.national.com 6 LMV716 Typical Performance Characteristics Unless otherwise specified, V+ 3.3V, TJ = 25˚C. CMRR vs. Frequency Crosstalk Rejection (Continued) 20179536 20179537 Inverting Large Signal Pulse Response Inverting Small Signal Pulse Response 20179535 20179533 Non-Inverting Large Signal Pulse Response Non-Inverting Small Signal Pulse Response 20179534 20179532 7 www.national.com LMV716 Typical Performance Characteristics Unless otherwise specified, V+ 3.3V, TJ = 25˚C. Open Loop Frequency vs. RL (Continued) Open Loop Frequency Response over Temperature 20179521 20179522 Open Loop Frequency Response vs. CL Open Loop Frequency Response vs. CL 20179523 20179528 Voltage Noise vs. Frequency 20179524 www.national.com 8 LMV716 Application Information With the low supply current of only 1.6 mA, the LMV716 offers users the ability to maximize battery life. This makes the LMV716 ideal for battery powered systems. The LMV716’s rail-to-rail output swing provides the maximum possible dynamic range at the output. This is particularly important when operating on low supply voltages. CAPACITIVE LOAD TOLERANCE The LMV716, when in a unity-gain configuration, can directly drive large capacitive loads in unity-gain without oscillation. The unity-gain follower is the most sensitive configuration to capacitive loading; direct capacitive loading reduces the phase margin of amplifiers. The combination of the amplifier’s output impedance and the capacitive load induces phase lag. This results in either an underdamped pulse response or oscillation. To drive a heavier capacitive load, the circuit in Figure 1 can be used. 20179509 FIGURE 2. Indirectly Driving a Capacitive Load with DC Accuracy DIFFERENCE AMPLIFIER The difference amplifier allows the subtraction of two voltages or, as a special case, the cancellation of a signal common to two inputs. It is useful as a computational amplifier in making a differential to single-ended conversion or in rejecting a common mode signal. 20179507 FIGURE 1. Indirectly Driving a Capacitive Load using Resistive Isolation In Figure 1, the isolation resistor RISO and the load capacitor CL form a pole to increase stability by adding more phase margin to the overall system. The desired performance depends on the value of RISO. The bigger the RISO resistor value, the more stable VOUT will be. The circuit in Figure 2 is an improvement to the one in Figure 1 because it provides DC accuracy as well as AC stability. If there were a load resistor in Figure 1, the output would be voltage divided by RISO and the load resistor. Instead, in Figure 2, RF provides the DC accuracy by using feedforward techniques to connect VIN to RL. Due to the input bias current of the LMV716, the designer must be cautious when choosing the value of RF. CF and RISO serve to counteract the loss of phase margin by feeding the high frequency component of the output signal back to the amplifier’s inverting input, thereby preserving phase margin in the overall feedback loop. Increased capacitive drive is possible by increasing the value of CF. This in turn will slow down the pulse response. 20179510 FIGURE 3. Difference Amplifier 9 www.national.com LMV716 Application Information (Continued) SINGLE-SUPPLY INVERTING AMPLIFIER There may be cases where the input signal going into the amplifier is negative. Because the amplifier is operating in single supply voltage, a voltage divider using R3 and R4 is implemented to bias the amplifier so the inverting input signal is within the input common voltage range of the amplifier. The capacitor C1 is placed between the inverting input and resistor R1 to block the DC signal going into the AC signal source, VIN. The values of R1 and C1 affect the cutoff frequency, fc = 1⁄2π R1C1. As a result, the output signal is centered around mid-supply (if the voltage divider provides V+/2 at the non-inverting input). The output can swing to both rails, maximizing the signal-to-noise ratio in a low voltage system. Three-Op-Amp Instrumentation Amplifier A typical instrumentation amplifier is shown in Figure 5. 20179542 FIGURE 5. Three-Op-Amp Instrumentation Amplifier There are two stages in this configuration. The last stage, the output stage, is a differential amplifier. In an ideal case the two amplifiers of the first stage, the input stage, would be set up as buffers to isolate the inputs. However they cannot be connected as followers due to the mismatch of real amplifiers. The circuit in Figure 5 utilizes a balancing resistor between the two amplifiers to compensate for this mismatch. The product of the two stages of gain will be the gain of the instrumentation amplifier circuit. Ideally, the CMRR should be infinite. However the output stage has a small non-zero common mode gain which results from resistor mismatch. In the input stage of the circuit, current is the same across all resistors. This is due to the high input impedance and low input bias current of the LMV716. With the node equations we have: 20179515 FIGURE 4. Single-supply Inverting Amplifier INSTRUMENTATION AMPLIFIER Measurement of very small signals with an amplifier requires close attention to the input impedance of the amplifier, the overall signal gain from both inputs to the output, as well as, the gain from each input to the output. This is because we are only interested in the difference of the two inputs and the common signal is considered noise. A classic solution is an instrumentation amplifier. Instrumentation amplifiers have a finite, accurate, and stable gain. Also they have extremely high input impedances and very low output impedances. Finally they have an extremely high CMRR so that the amplifier can only respond to the differential signal. (1) By Ohm’s Law: (2) However: (3) So we have: (4) www.national.com 10 LMV716 Application Information (Continued) Now looking at the output of the instrumentation amplifier: Low Pass Filter The following shows a very simple low pass filter. (5) Substituting from Equation (4): (6) This shows the gain of the instrumentation amplifier to be: −K(2a+1) Typical values for this circuit can be obtained by setting: a = 12 and K = 4. This results in an overall gain of −100. Three LMV716 amplifiers are used along with 1% resistors to minimize resistor mismatch. Resistors used to build the circuit are: R1 = 21.6 kΩ, R11 = 1.8 kΩ, R2 = 2.5 kΩ with K = 40 and a = 12. This results in an overall gain of −K(2a+1) = −1000. Two-Op-Amp Instrumentation Amplifier A two-op-amp instrumentation amplifier can also be used to make a high-input impedance DC differential amplifier Figure 6). As in the three op amp circuit, this instrumentation amplifier requires precise resistor matching for good CMRR. R4 should be equal to R1, and R3 should equal R2. FIGURE 7. Low Pass Filter The transfer function can be expressed as follows: By KCL: 20179553 (7) Simplifying this further results in: (8) or 20179513 (9) Now, substituting ω=2πf, so that the calculations are in f(Hz) rather than in ω(rad/s), and setting the DC gain and (10) set: FIGURE 6. Two-Op-Amp Instrumentation Amplifier ACTIVE FILTERS Active filters are circuits with amplifiers, resistors, and capacitors. The use of amplifiers instead of inductors, which are used in passive filters, enhances the circuit performance while reducing the size and complexity of the filter. The simplest active filters are designed using an inverting op amp configuration where at least one reactive element has been added to the configuration. This means that the op amp will provide "frequency-dependent" amplification, since reactive elements are frequency dependent devices. (11) Low pass filters are known as lossy integrators because they only behave as integrators at higher frequencies. The general form of the bode plot can be predicted just by looking at the transfer function. When the f/fO ratio is small, the capacitor is, in effect, an open circuit and the amplifier behaves at a set DC gain. Starting at fO, which is the −3 dB corner, the capacitor will have the dominant impedance and hence the circuit will behave as an integrator and the signal will be attenuated and eventually cut. The bode plot for this filter is shown in Figure 8. 11 www.national.com LMV716 Application Information (Continued) (14) Looking at the transfer function, it is clear that when f/fO is small, the capacitor is open and therefore, no signal is getting to the amplifier. As the frequency increases the amplifier starts operating. At f = fO the capacitor behaves like a short circuit and the amplifier will have a constant, high frequency gain of HO. Figure 10 shows the transfer function of this high pass filter. 20179559 FIGURE 8. Low Pass Filter Transfer Function High Pass Filter The transfer function of a high pass filter can be derived in much the same way as the previous example. A typical first order high pass filter is shown below: 20179564 FIGURE 10. High Pass Filter Transfer Function Band Pass Filter Combining a low pass filter and a high pass filter will generate a band pass filter. Figure 11 offers an example of this type of circuit. 20179560 FIGURE 9. High Pass Filter Writing the KCL for this circuit : (V1 denotes the voltage between C and R1) (12) FIGURE 11. Band Pass Filter (13) Solving these two equations to find the transfer function and using: 20179566 In this network the input impedance forms the high pass filter while the feedback impedance forms the low pass filter. If the designer chooses the corner frequencies so that f1 < f2, then all the frequencies between, f1 ≤ f ≤ f2, will pass through the filter while frequencies below f1 and above f2 will be cut off. The transfer function can be easily calculated using the same methodology as before and is shown in Figure 12. (high frequency gain) Which gives: and (15) www.national.com 12 LMV716 Application Information Where (Continued) The transfer function of each filter needs to be calculated. The derivations will be more trivial if each stage of the filter is shown on its own. The three components are: (16) 20179570 20179568 FIGURE 12. Band Pass Filter Transfer Function STATE VARIABLE ACTIVE FILTER State variable active filters are circuits that can simultaneously represent high pass, band pass, and low pass filters. The state variable active filter uses three separate amplifiers to achieve this task. A typical state variable active filter is shown in Figure 13. The first amplifier in the circuit is connected as a gain stage. The second and third amplifiers are connected as integrators, which means they behave as low pass filters. The feedback path from the output of the third amplifier to the first amplifier enables this low frequency signal to be fed back with a finite and fairly low closed loop gain. This is while the high frequency signal on the input is still gained up by the open loop gain of the first amplifier. This makes the first amplifier a high pass filter. The high pass signal is then fed into a low pass filter. The outcome is a band pass signal, meaning the second amplifier is a band pass filter. This signal is then fed into the third amplifiers input and so, the third amplifier behaves as a simple low pass filter. 20179571 For A1 the relationship between input and output is: (17) This relationship depends on the output of all the filters. The input-output relationship for A2 can be expressed as: (18) And finally this relationship for A3 is as follows: (19) Re-arranging these equations, one can find the relationship between VO and VIN (transfer function of the low pass filter), VO1 and VIN (transfer function of the high pass filter), and VO2 and VIN (transfer function of the band pass filter) These relationships are as follows: 20179569 FIGURE 13. State Variable Active Filter 13 www.national.com LMV716 Application Information Low Pass Filter (Continued) Designing a band pass filter with a center frequency of 10 kHz and Quality Factor of 5.5 To do this, first consider the Quality Factor. It is best to pick convenient values for the capacitors. C2 = C3 = 1000 pF. Also, choose R1 = R4 = 30 kΩ. Now values of R5 and R6 need to be calculated. With the chosen values for the capacitors and resistors, Q reduces to: (20) High Pass Filter (24) or R5 = 10R6 R6 = 1.5 kΩ (25) R5 = 15 kΩ Also, for f = 10 kHz, the center frequency is ωc = 2πf = 62.8 kHz. Using the expressions above, the appropriate resistor values will be R2 = R3 = 16 kΩ. The DC gain of this circuit is: (21) Band Pass Filter (26) (22) The center frequency and Quality Factor for all of these filters is the same. The values can be calculated in the following manner: (23) www.national.com 14 LMV716 5 MHz, Low Noise, RRO, Dual Operational Amplifier with CMOS Input Physical Dimensions inches (millimeters) unless otherwise noted 8-Pin MSOP NS Package Number MUA08A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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