Precision, Very Low Noise, Low Input Bias Current Operational Amplifiers
AD8671/AD8672/AD8674
FEATURES
Very low noise: 2.8 nV/√Hz, 77 nV p-p Wide bandwidth: 10 MHz Low input bias current: 12 nA max Low offset voltage: 75 μV max High open-loop gain: 120 dB min Low supply current: 3 mA per amplifier Dual-supply operation: ±5 V to ±15 V Unity-gain stable No phase reversal
NC 1 –IN 2 +IN 3
PIN CONFIGURATIONS
8
NC V+
03718-B-001
NC 1 –IN 2 +IN 3
8
NC
AD8671
7
NC = NO CONNECT
NC = NO CONNECT
Figure 1. 8-Lead SOIC_N (R-8)
Figure 2. 8-Lead MSOP (RM-8)
OUT A 1 –IN A 2
8
V+ OUT B
03718-B-003
OUT A 1 –IN A 2 +IN A 3
8
V+
AD8672
7
PLL filters Filters for GPS Instrumentation Sensors and controls Professional quality audio
Figure 3. 8-Lead SOIC-N (R-8)
Figure 4. 8-Lead MSOP (RM-8)
OUT A 1 –IN A 2
14 OUT D 13 –IN D
OUT A 1 –IN A 2 +IN A 3 V+ 4
14 OUT D 13 –IN D
GENERAL DESCRIPTION
The AD8671/AD8672/AD8674 are very high precision amplifiers featuring very low noise, very low offset voltage and drift, low input bias current, 10 MHz bandwidth, and low power consumption. Outputs are stable with capacitive loads of over 1000 pF. Supply current is less than 3 mA per amplifier at 30 V. The AD8671/AD8672/AD8674’s combination of ultralow noise, high precision, speed, and stability is unmatched. The MSOP version of the AD8671/AD8672 requires only half the board space of comparable amplifiers. Applications for these amplifiers include high quality PLL filters, precision filters, medical and analytical instrumentation, precision power supply controls, ATE, data acquisition, and precision controls as well as professional quality audio. The AD8671/AD8672/AD8674 are specified over the extended industrial temperature range (–40°C to +125°C). The AD8671/AD8672 are available in the 8-lead SOIC and 8-lead MSOP packages. The AD8674 is available in 14-lead SOIC and 14-lead TSSOP packages. Surface-mount devices in MSOP packages are available in tape and reel only.
+IN A 3 V+ 4
AD8674
12 +IN D
AD8674
12 +IN D
TOP VIEW 11 V– +IN B 5 (Not to Scale) 10 +IN C
03718-B-005
TOP VIEW 11 V– +IN B 5 (Not to Scale) 10 +IN C –IN B 6 OUT B 7
9 8
–IN B 6 OUT B 7
9 8
–IN C OUT C
–IN C OUT C
Figure 5. 14-Lead SOIC_N (R-14)
Figure 6. 14-Lead TSSOP (RU-14)
Rev. 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. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 © 2005 Analog Devices, Inc. All rights reserved.
03718-B-006
03718-B-004
APPLICATIONS
+IN A 3
TOP VIEW 6 –IN B (Not to Scale) 5 +IN B V– 4
OUT B TOP VIEW 6 –IN B (Not to Scale) 5 +IN B V– 4
7
AD8672
03718-B-002
TOP VIEW 6 OUT (Not to Scale) V– 4 5 NC
V+ TOP VIEW 6 OUT (Not to Scale) V– 4 5 NC
7
AD8671
AD8671/AD8672/AD8674 TABLE OF CONTENTS
Specifications..................................................................................... 3 Electrical Characteristics, ±5.0 V ............................................... 3 Electrical Characteristics, ±15 V ................................................ 4 Absolute Maximum Ratings............................................................ 5 ESD CAUTION ............................................................................ 5 Typical Performance Characteristics ............................................. 6 Applications..................................................................................... 11 Unity-Gain Follower Applications ........................................... 11 Output Phase Reversal............................................................... 11 Total Noise vs. Source Resistance............................................. 11 Total Harmonic Distortion (THD) and Noise ....................... 12 Driving Capacitive Loads.......................................................... 12 GPS Receiver............................................................................... 13 Band-Pass Filter.......................................................................... 13 PLL Synthesizers and Loop Filters ........................................... 13 Outline Dimensions ....................................................................... 14 Ordering Guide .......................................................................... 16
REVISION HISTORY
6/05—Rev. B to Rev. C Changes to Figure 6...................................................................... 1 Updated Outline Dimensions ................................................... 14 Changes to Ordering Guide ...................................................... 16 4/04—Rev. A to Rev. B Changes to Figure 32.................................................................. 11 Changes to Figures 36, 37, and 38 ............................................ 12 1/04—Rev. 0 to Rev. A Added AD8672 and AD8674 parts ..............................Universal Changes to Specifications ............................................................ 3 Deleted Figure 3............................................................................ 6 Changes to Figures 7, 8, and 9 .................................................... 6 Changes to Figure 37.................................................................. 12 Added new Figure 32 ................................................................. 10
Rev. C | Page 2 of 16
AD8671/AD8672/AD8674 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS, ±5.0 V
VS = ±5.0 V, VCM = 0 V, TA = 25°C, unless otherwise noted. Table 1.
Parameter INPUT CHARACTERISTICS Offset Voltage Offset Voltage Drift AD8671 AD8672/AD8674 Input Bias Current Symbol VOS ∆VOS/∆T –40°C < TA < +125°C –40°C < TA < +125°C Conditions Min Typ 20 30 0.3 0.3 +3 +5 +8 +6 +6 +8 120 6000 6.25 7.5 3.5 15 +4.0 –3.9 +3.9 –3.8 ±10 Max 75 125 0.5 0.8 +12 +20 +40 +12 +20 +40 +2.5 Unit μV μV μV/°C μV/°C nA nA nA nA nA nA V dB V/mV pF pF GΩ MΩ V V V V mA
IB +25°C < TA < +125°C –40°C < TA < +125°C
Input Offset Current
IOS +25°C < TA < +125°C –40°C < TA < +125°C
Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Input Capacitance, Common Mode Input Capacitance, Differential Mode Input Resistance, Common Mode Input Resistance, Differential Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Output Voltage High Output Voltage Low Output Current POWER SUPPLY Power Supply Rejection Ratio AD8671/AD8672 AD8674 Supply Current/Amplifier DYNAMIC PERFORMANCE Slew Rate Settling Time Gain Bandwidth Product NOISE PERFORMANCE Peak-to-Peak Noise Voltage Noise Density Current Noise Density Channel Separation AD8672/AD8674
CMRR AVO CINCM CINDM RIN RINDM VOH VOL VOH VOL IOUT PSRR
VCM = –2.5 V to +2.5 V RL = 2 kΩ, VO = –3 V to +3 V
–12 –20 –40 –12 –20 –40 –2.5 100 1000
RL = 2 kΩ, –40°C to +125°C RL = 2 kΩ, –40°C to +125°C RL = 600 Ω RL = 600 Ω
+3.8 +3.7
–3.8 –3.7
VS = ±4 V to ±18 V 110 106 130 115 3 dB dB mA mA V/μs μs μs MHz 100 3.8 nV p-p nV/√Hz pA/√Hz dB dB
ISY
VO = 0 V –40°C < TA < +125°C RL = 2 kΩ To 0.1% (4 V step, G = 1) To 0.01% (4 V step, G = 1)
3.5 4.2
SR tS GBP en p-p en in CS
4 1.4 5.1 10 77 2.8 0.3 –130 –105
0.1 Hz to 10 Hz f = 1 kHz f = 1 kHz f = 1 kHz f = 10 kHz
Rev. C | Page 3 of 16
AD8671/AD8672/AD8674
ELECTRICAL CHARACTERISTICS, ±15 V
VS = ±15 V, VCM = 0 V, TA = 25°C, unless otherwise noted. Table 2.
Parameter INPUT CHARACTERISTICS Offset Voltage Offset Voltage Drift AD8671 AD8672/AD8674 Input Bias Current Symbol VOS ∆VOS/∆T –40°C < TA < +125°C –40°C < TA < +125°C Conditions Min Typ 20 30 0.3 0.3 +3 +5 +8 +6 +6 +8 120 6000 6.25 7.5 3.5 15 +13.8 –13.8 +12.3 –12.4 ±20 ±30 Max 75 125 0.5 0.8 +12 +20 +40 +12 +20 +40 +12 Unit μV μV μV/°C μV/°C nA nA nA nA nA nA V dB V/mV pF pF GΩ MΩ V V V V mA mA
IB +25°C < TA < +125°C –40°C < TA < +125°C
Input Offset Current
IOS +25°C < TA < +125°C –40°C < TA < +125°C
Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Input Capacitance, Common Mode Input Capacitance, Differential Mode Input Resistance, Common Mode Input Resistance, Differential Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Output Voltage High Output Voltage Low Output Current Short Circuit Current POWER SUPPLY Power Supply Rejection Ratio AD8671/AD8672 AD8674 Supply Current/Amplifier DYNAMIC PERFORMANCE Slew Rate Settling Time Gain Bandwidth Product NOISE PERFORMANCE Peak-to-Peak Noise Voltage Noise Density Current Noise Density Channel Separation AD8672/AD8674
CMRR AVO CINCM CINDM RIN RINDM VOH VOL VOH VOL IOUT ISC PSRR
VCM = –12 V to +12 V RL = 2 kΩ, VO = –10 V to +10 V
–12 –20 –40 –12 –20 –40 –12 100 1000
RL = 2 kΩ, –40°C to +125°C RL = 2 kΩ, –40°C to +125°C RL = 600 Ω RL = 600 Ω
+13.2 +11
–13.2 –11
VS = ±4 V to ±18 V 110 106 130 115 3 dB dB mA mA V/μs μs μs MHz 100 3.8 nV p-p nV/√Hz pA/√Hz dB dB
ISY
VO = 0 V –40°C 1 V) are applied at the positive terminal of amplifiers (such as the OP27, LT1007, OPA227, and AD8671) with back-to-back diodes at the input stage, the use of a resistor in the feedback loop is recommended to avoid having the amplifier load the signal generator. The feedback resistor, RF, should be at least 500 Ω. However, if large values must be used for RF, a small capacitor, CF, should be inserted in parallel with RF to compensate for the pole introduced by the input capacitance and RF. Figure 32 shows the uncompensated output response with a 10 kΩ resistor in the feedback and the compensated response with CF = 15 pF.
OUTPUT UNCOMPENSATED OUTPUT COMPENSATED REF1 +OVER 23.23% CH2 +OVER 7.885%
VIN VSY = ±15V
VOLTAGE (1V/DIV)
VOUT
TIME (10μs/DIV)
Figure 33. Output Phase Reversal
TOTAL NOISE VS. SOURCE RESISTANCE
The low input voltage noise of the AD8671/AD8672/AD8674 makes them a great choice for applications with low source resistance. However, because they have low input current noise, they can also be used in circuits with substantial source resistance. Figure 34 shows the voltage noise, current noise, thermal noise, and total rms noise of the AD8671 as a function of the source resistance.
03718-B-032
VOLTAGE (1V/DIV)
TIME (100ns/DIV)
Figure 32. Transient Output Response
For RS < 475 Ω, the input voltage noise, en, dominates. For 475 Ω < RS < 412 kΩ, thermal noise dominates. For RS > 412 kΩ, the input current noise dominates.
1000
OUTPUT PHASE REVERSAL
TOTAL NOISE (nV/√Hz)
Phase reversal is a change of polarity in the amplifier transfer function that occurs when the input voltage exceeds the supply voltage. The AD8671/AD8672/AD8674 do not exhibit phase reversal even when the input voltage is 1 V beyond the supplies.
C 100
in
10 en_t A 1 10 100 1k 10k 100k 1M SOURCE RESISTANCE ( Ω) (4kR ST)1/2 B
03718-B-034
en
Figure 34. Noise vs. Source Resistance
Rev. C | Page 11 of 16
03718-B-033
AD8671/AD8672/AD8674
TOTAL HARMONIC DISTORTION (THD) AND NOISE
The AD8671/AD8672/AD8674 exhibit low total harmonic distortion (THD) over the entire audio frequency range. This makes them suitable for applications with high closed-loop gains, including audio applications. Figure 35 shows approximately 0.0006% of THD + N in a positive unity gain, the worst-case configuration for distortion.
0.1000 0.0500 0.0200 0.0100 VS = ±5V VIN = 2.5V RL = 600Ω
VOLTAGE (500mV/DIV)
VSY = ±15V RL = 2kΩ CL = 1nF VIN = 100mV AV = +1 CH2 +OVER 39.80% CH2 –OVER 39.80%
TIME (10μs/DIV)
PERCENTAGE
0.0050 0.0020 0.0010 0.0005 0.0002 0.0001 20
03718-B-035
Figure 36. AD8671 Capacitive Load Drive
RF
LT1007
500Ω
AD8671
RG 500Ω
CF 220pF
VCC
RS 10Ω VIN VEE
50 100 200 500 Hz 1k 2k 5k 10k 20k
CL 1nF
Figure 35. Total Harmonic Distortion and Noise
DRIVING CAPACITIVE LOADS
The AD8671/AD8672/AD8674 can drive large capacitive loads without causing instability. However, when configured in unity gain, driving very large loads can cause unwanted ringing or instability. Figure 36 shows the output of the AD8671 with a capacitive load of 1 nF. If heavier loads are used in low closed-loop gain or unity-gain configurations, it is recommended to use external compensation as shown in the circuit in Figure 37. This technique reduces the overshoot and prevents the op amp from oscillation. The trade-off of this circuit is a reduction in output swing. However, a great added benefit stems from the fact that the input signal and the op amp’s noise are filtered, and thus the overall output noise is kept to a minimum. The output response of the circuit is shown in Figure 38.
VOLTAGE (100mV/DIV)
Figure 37. Recommended Capacitive Load Circuit
VSY = ±15V RL = 2kΩ CL = 1nF CF = 220pF VIN = 100mV AV = +2
CH2 +OVER 5.051% CH2 –OVER 6.061%
TIME (10μs/DIV)
Figure 38. Compensated Load Drive
Rev. C | Page 12 of 16
03718-B-038
03718-B-037
RL 2kΩ
03718-B-036
AD8671/AD8672/AD8674
ADC LOW NOISE OP AMP BAND-PASS FILTER MIXER DEMODULATOR LOW-PASS FILTER VGA
AD8671
AD8671
AD831
AD630
AD8610
AD8369
AD10200
CODE GENERATOR
Figure 39. Simplified Block Diagram of a GPS Receiver
GPS RECEIVER
GPS receivers require low noise to minimize RF effects. The precision of the AD8671 makes it an excellent choice for such applications. Its very low noise and wide bandwidth make it suitable for band-pass and low-pass filters without the penalty of high power consumption. Figure 39 shows a simplified block diagram of a GPS receiver. The next section details the design equations.
The band-pass response is shown in Figure 41.
VS = ±15V
BAND-PASS FILTER
Filters are useful in many applications; for example, band-pass filters are used in GPS systems, as discussed in the previous section. Figure 40 shows a second-order band-pass KRC filter.
R3 2.25kΩ VCC
200μV/DIV
03718-B-039
100
1k
10k Hz
100k
1M
10M
Figure 41. Band-Pass Response
R1
2.25kΩ VIN C2 1nF
C2 1nF R2 2.25kΩ
PLL SYNTHESIZERS AND LOOP FILTERS
Phase-lock loop filters are used in AM/FM modulation.
RB 18kΩ
VEE RA 10kΩ
03718-B-040
Figure 40. Band-Pass KRC Filter
The equal component topology yields a center frequency
fo =
2 2πRC 2 4−K
Loop filters in PLL design require accuracy and care in their implementation. The AD8671/AD8672/AD8674 are ideal candidates for such filter design; the low offset voltage and low input bias current minimize the output error. In addition to the excellent dc specifications, the AD8671/AD8672/AD8674 have a unique performance at high frequencies; the high open-loop gain and wide bandwidth allow the user to design a filter with a high closed-loop gain if desirable. To optimize the filter design, it is recommended to use small value resistors to minimize the thermal noise. A simple example is shown in Figure 42.
R1 10kΩ VCC C1 1nF
and Q = where:
PHASE DETECTOR
CHARGE PUMP
VCO
K =1+
IN
Figure 42. PLL Filter Simplified Block Diagram
Rev. C | Page 13 of 16
03718-B-042
RB RA
D VEE
03718-B-041
AD8671/AD8672/AD8674 OUTLINE DIMENSIONS
5.00 (0.1968) 4.80 (0.1890)
8 5 4
4.00 (0.1574) 3.80 (0.1497) 1
6.20 (0.2440) 5.80 (0.2284)
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040)
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) × 45° 0.25 (0.0099)
0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE
8° 0.25 (0.0098) 0° 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MS-012-AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
Figure 43. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches)
3.00 BSC
8
5
3.00 BSC
1
4.90 BSC
4
PIN 1 0.65 BSC 1.10 MAX 8° 0° 0.80 0.60 0.40
0.15 0.00 0.38 0.22 COPLANARITY 0.10
0.23 0.08 SEATING PLANE
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 44. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
Rev. C | Page 14 of 16
AD8671/AD8672/AD8674
8.75 (0.3445) 8.55 (0.3366)
14 1 8 7
4.00 (0.1575) 3.80 (0.1496)
6.20 (0.2441) 5.80 (0.2283)
0.25 (0.0098) 0.10 (0.0039)
1.27 (0.0500) BSC
1.75 (0.0689) 1.35 (0.0531)
0.50 (0.0197) × 45° 0.25 (0.0098)
COPLANARITY 0.10
0.51 (0.0201) 0.31 (0.0122)
SEATING PLANE
8° 0.25 (0.0098) 0° 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MS-012-AB CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
Figure 45. 14-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown in millimeters and (inches)
5.10 5.00 4.90
14
8
4.50 4.40 4.30
1 7
6.40 BSC
PIN 1 1.05 1.00 0.80 0.65 BSC 1.20 MAX 0.15 0.05 0.30 0.19 0.20 0.09 8° 0° 0.75 0.60 0.45
SEATING COPLANARITY PLANE 0.10
COMPLIANT TO JEDEC STANDARDS MO-153-AB-1
Figure 46. 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown in millimeters
Rev. C | Page 15 of 16
AD8671/AD8672/AD8674
ORDERING GUIDE
Model AD8671AR AD8671AR-REEL AD8671AR-REEL7 AD8671ARZ 1 AD8671ARZ-REEL1 AD8671ARZ-REEL71 AD8671ARM-R2 AD8671ARM-REEL AD8671ARMZ-R21 AD8671ARMZ-REEL1 AD8672AR AD8672AR-REEL AD8672AR-REEL7 AD8672ARZ1 AD8672ARZ-REEL1 AD8672ARZ-REEL71 AD8672ARM-R2 AD8672ARM-REEL AD8672ARMZ-R21 AD8672ARMZ-REEL1 AD8674AR AD8674AR-REEL AD8674AR-REEL7 AD8674ARZ1 AD8674ARZ-REEL1 AD8674ARZ-REEL71 AD8674ARU AD8674ARU-REEL AD8674ARUZ1 AD8674ARUZ-REEL1
1
Temperature Range –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C
Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead TSSOP 14-Lead TSSOP 14-Lead TSSOP 14-Lead TSSOP
Package Option R-8 R-8 R-8 R-8 R-8 R-8 RM-8 RM-8 RM-8 RM-8 R-8 R-8 R-8 R-8 R-8 R-8 RM-8 RM-8 RM-8 RM-8 R-14 R-14 R-14 R-14 R-14 R-14 RU-14 RU-14 RU-14 RU-14
Branding
BGA BGA A0V A0V
BHA BHA A0W A0W
Z = Pb-free part.
© 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D03718–0–6/05(C)
Rev. C | Page 16 of 16