AD605BR

AD605_06 AD | Alldatasheet

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Technical content

Dual, Low Noise, Single-Supply Variable Gain Amplifier AD605 Rev. D 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. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved.

FEATURES

2 independent linear-in-dB channels Input noise at maximum gain: 1.8 nV/√Hz, 2.7 pA/√Hz Bandwidth: 40 MHz (–3 dB) Differential input Absolute gain range programmable –14 dB to +34 dB (FBK shorted to OUT) through 0 dB to 48 dB (FBK open) Variable gain scaling: 20 dB/V through 40 dB/V Stable gain with temperature and supply variations Single-ended unipolar gain control Output common mode independently set Power shutdown at lower end of gain control Single 5 V supply Low power: 90 mW/channel Drives ADCs directly

APPLICATIONS

Ultrasound and sonar time-gain controls High performance AGC systems Signal measurement FUNCTIONAL BLOCK DIAGRAM PRECISION PASSIVE INPUT ATTENUATOR FIXED GAIN AMPLIFIER +34.4dB DIFFERENTIAL ATTENUATOR 0 TO –48.4dB OUT VOCM VGN VREF +IN –IN GAIN CONTROL AND SCALING FBK AD605 00541-001 Figure 1. GENERAL DESCRIPTION The AD605 is a low noise, accurate, dual channel, linear-in-dB variable gain amplifier, optimized for any application requiring high performance, wide bandwidth variable gain control. Operating from a single 5 V supply, the AD605 provides differential inputs and unipolar gain control for ease of use. Added flexibility is achieved with a user-determined gain range and an external reference input that provides user-determined gain scaling (dB/V). The high performance linear-in-dB response of the AD605 is achieved with the differential input, single-supply, exponential amplifier (DSX-AMP) architecture. Each of the DSX-AMPs comprise a variable attenuator of 0 dB to −48.4 dB followed by a high speed fixed gain amplifier. The attenuator is based on a 7-stage R-1.5R ladder network. The attenuation between tap points is 6.908 dB, and 48.360 dB for the entire ladder network. The DSX-AMP architecture results in 1.8 nV/√Hz input noise spectral density and accepts a ±2.0 V input signal when VOCM is biased at VP/2. Each independent channel of the AD605 provides a gain range of 48 dB that can be optimized for the application. Gain ranges between −14 dB to +34 dB and 0 dB to +48 dB can be selected by a single resistor between Pin FBK and Pin OUT. The lower and upper gain ranges are determined by shorting Pin FBK to Pin OUT, or leaving Pin FBK unconnected, respectively. The two channels of the AD605 can be cascaded to provide 96 dB of very accurate gain range in a monolithic package. The gain control interface provides an input resistance of approximately 2 MΩ and scale factors from 20 dB/V to 30 dB/V for a VREF input voltage of 2.5 V to 1.67 V , respectively. Note that scale factors up to 40 dB/V are achievable with reduced accuracy for scales above 30 dB/V . The gain scales linearly in dB with control voltages (VGN) of 0.4 V to 2.4 V for the 20 dB/V scale and 0.20 V to 1.20 V for the 40 dB/V scale. When VGN is <50 mV , the amplifier is powered down to draw 1.9 mA. Under normal operation, the quiescent supply current of each amplifier channel is only 18 mA. The AD605 is available in 16-lead PDIP and 16-lead SOIC_N and is guaranteed for operation over the −40°C to +85°C temperature range.

Rev. D | Page 2 of 20 TABLE OF CONTENTS

REVISION HISTORY

1/06—Rev. C to Rev. D 7/04—Rev. B to Rev. C

Rev. D | Page 3 of 20 SPECIFICATIONS Each channel @ TA = 25°C, VS = 5 V , RS = 50 Ω, RL = 500 Ω, CL = 5 pF, VREF = 2.5 V (scaling = 20 dB/V), −14 dB to +34 dB gain range, unless otherwise noted. Table 1. AD605A AD605B Parameter Conditions Min Typ Max Min Typ Max Unit INPUT CHARACTERISTICS Input Resistance 175 ± 40 175 ± 40 Ω Input Capacitance 3.0 3.0 pF Peak Input Voltage At minimum gain 2.5 ± 2.5 2.5 ± 2.5 V Input Voltage Noise VGN = 2.9 V 1.8 1.8 nV/√Hz Input Current Noise VGN = 2.9 V 2.7 2.7 pA/√Hz Noise Figure RS = 50 Ω, f = 10 MHz, VGN = 2.9 V 8.4 8.4 dB RS = 200 Ω, f = 10 MHz, VGN = 2.9 V 12 12 dB Common-Mode Rejection Ratio f = 1 MHz, VGN = 2.65 V −20 −20 dB OUTPUT CHARACTERISTICS −3 dB Bandwidth Constant with gain 40 40 MHz Slew Rate VGN = 1.5 V, Output = 1 V step 170 170 V/μs Output Signal Range RL ≥ 500 Ω 2.5 ± 1.5 2.5 ± 1.5 V Output Impedance f = 10 MHz 2 2 Ω Output Short-Circuit Current ±40 ±40 mA Harmonic Distortion VGN = 1 V, VOUT = 1 V p-p HD2 f = 1 MHz −64 −64 dBc HD3 f = 1 MHz −68 −68 dBc HD2 f = 10 MHz −51 −51 dBc HD3 f = 10 MHz −53 −53 dBc Two-Tone Intermodulation Distortion (IMD) RS = 0 Ω, VGN = 2.9 V, VOUT = 1 V p-p f = 1 MHz −72 −72 dBc f = 10 MHz −60 −60 dBc 1 dB Compression Point f = 10 MHz, VGN = 2.9 V, output referred +15 +15 dBm Third-Order Intercept f = 10 MHz, VGN = 2.9 V, VOUT = 1 V p-p, input referred −1 −1 dBm Channel-to-Channel Crosstalk Ch1: VGN = 2.65 V, inputs shorted, Ch2: VGN = 1.5 V (mid gain), f = 1 MHz, VOUT = 1 V p-p −70 −70 dB Group Delay Variation 1 MHz < f < 10 MHz, full gain range ±2.0 ±2.0 ns VOCM Input Resistance 45 45 kΩ ACCURACY Absolute Gain Error Gain Scaling Error 0.4 V < VGN < 2.4 V ±0.25 ±0.25 dB/V Output Offset Voltage VREF = 2.500 V, VOCM = 2.500 V −50 ±30 +50 –50 ±30 +50 mV Output Offset Variation VREF = 2.500 V, VOCM = 2.500 V 30 95 30 50 mV

Rev. D | Page 4 of 20 AD605A AD605B Parameter Conditions Min Typ Max Min Typ Max Unit GAIN CONTROL INTERFACE Gain Scaling Factor VREF = 2.5 V, 0.4 V < VGN < 2.4 V 19 20 21 19 20 21 dB/V VREF = 1.67 V 30 30 dB/V Gain Range FBK short to OUT −14 to +34 −14 to +34 dB FBK open 0 to 48 0 to 48 dB Input Bias Current −0.4 −0.4 μA Input Resistance 2 2 MΩ Response Time 48 dB gain change 0.2 0.2 μs POWER SUPPLY Power Dissipation 90 90 mW VREF Input Resistance 10 10 kΩ Quiescent Supply Current VPOS 18 23 18 23 mA Power Down VPOS, VGN < 50 mV 1.9 3.0 1.9 3.0 mA Power-Up Response Time 48 dB gain, VOUT = 2 V p-p 0.6 0.6 μs Power-Down Response Time 0.4 0.4 μs

Rev. D | Page 5 of 20 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Rating Supply Voltage +VS Pin 12, Pin 13 (with Pin 4, Pin 5 = 0 V) 6.5 V Input Voltage Pin 1 to Pin 3, Pin 6 to Pin 9, Pin 16 VPOS, 0 Internal Power Dissipation 16-Lead PDIP 1.4 W 16-Lead SOIC_N 1.2 W Operating Temperature Range −40°C to +85°C Storage Temperature Range −65°C to +150°C Lead Temperature, Soldering 60 sec 300°C Thermal Resistance θJA 16-Lead PDIP 85°C/W 16-Lead SOIC_N 100°C/W Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electros tatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge wi thout detection. Although this product features proprietary ESD protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

Figure 2. Pin Configuration Table 3. Pin Function Descriptions 1 VGN1 CH1 Gain-Control Input and Power-Down Pin. If grounded, device is off; otherwise, positive voltage increases gain. 8 VGN2 CH2 Gain-Control Input and Power-Down Pin. If grounded, device is off; otherwise, positive voltage increases gain. 9 VOCM Input to This Pin Defines Common-Mode Voltage for OUT1 and OUT2. 11 FBK2 Feedback Pin That Selects Gain Range of CH2. 14 FBK1 Feedback Pin That Selects Gain Range of CH1. 16 VREF Input to This Pin Sets Gain Scaling for Both Channels: 2.5 V = 20 dB/V, and 1.67 V = 30 dB/V.

The AD605 is a dual channel, low noise variable gain amplifier. Figure 35 shows the simplified block diagram of one channel.

• Precision passive attenuator (differential ladder)
• Gain control block
• VOCM buffer with supply splitting resistors R3 and R4
• Active feedback amplifier1 (AFA) with gain setting resistors R1 and R2 The linear-in-dB gain response of the AD605 can generally be described by Equation 1. G (dB) = (Gain Scaling (dB/V)) × (Gain Control (V)) − where: FB = 0, if FBK-to-OUT are shorted. FB = 1, if FBK-to-OUT is open. Each channel provides between −14 dB to +34.4 dB through 0 dB to +48.4 dB of gain depending on the value of the resistance connected between Pin FBK and Pin OUT. The center 40 dB of gain is exactly linear-in-dB while the gain error increases at the top and bottom of the range. The gain is set by the gain control voltage (VGN). The VREF input establishes the gain scaling. The useful gain scaling range is between 20 dB/V and 40 dB/V for a VREF voltage of 2.5 V and 1.25 V , respectively. For example, if FBK to OUT were shorted and VREF were set to 2.50 V (to establish a gain scaling of 20 dB/V), the gain equation would simplify to G (dB) = (20 (dB/V)) × (VGN (V)) – 19 dB (2) The desired gain can then be achieved by setting the unipolar gain control (VGN) to a voltage within its nominal operating range of 0.25 V to 2.65 V (for 20 dB/V gain scaling). The gain is monotonic for a complete gain control range of 0.1 V to 2.9 V . Maximum gain can be achieved at a VGN of 2.9 V . Because the two channels are identical, only Channel 1 is used to describe their operation. VREF and VOCM are the only inputs that are shared by the two channels, and because they are normally ac grounds, crosstalk between the two channels is minimized. For highest gain scaling accuracy, VREF should have an external low impedance voltage source. For low accuracy 20 dB/V applications, the VREF input can be decoupled with a capacitor to ground. In this mode, the gain scaling is determined by the midpoint between +VCC and GND; therefore, care should be taken to control the supply voltage to 5 V . The input resistance looking into the VREF pin is 10 kΩ ± 20%. The AD605 is a single-supply circuit and the VOCM pin is used to establish the dc level of the midpoint of this portion of the circuit. VOCM needs only an external decoupling capacitor to ground to center the midpoint between the supply voltages (5 V , GND). However, if the dc level of the output is important to the user (see the an example), then VOCM can be specifically set. The input resistance looking into the VOCM pin is 45 kΩ ± 20%.

1 To understand the active-feedback amplifier topology, refer to the AD830

data sheet. The AD830 is a practical implementation of the idea. Figure 35. Simplified Block Diagram of a Single Channel of the AD605

Figure 37. Ideal Gain Curves vs. VREF response time to power the device on or off is less than 1 μs. depending on the gain control voltage. distributed gm stage. The second input (G2) is used for feedback. attenuator taps that is applied to a high-gain amplifier (A0). VATTEN is the effective voltage sensed on the attenuator. gm1/gm2 = 1.25; the overall gain is therefore 52.5 (34.4 dB). and independent control of the DSX common-mode voltage. limitation being the rather low slew rate of the VOCM buffer. offsets contributed by the DSX (see the AC Coupling section). amplifier that includes the active feedback amplifier.

Rev. D | Page 19 of 20 ORDERING GUIDE Model Temperature Range Package Description Package Option AD605AN −40°C to +85°C 16-Lead PDIP N-16 AD605ANZ1 −40°C to +85°C 16-Lead PDIP N-16 AD605AR −40°C to +85°C 16-Lead SOIC_N R-16 AD605AR-REEL −40°C to +85°C 16-Lead SOIC_N, 13" Reel R-16 AD605AR-REEL7 −40°C to +85°C 16-Lead SOIC_N, 7" Reel R-16 AD605ARZ1 −40°C to +85°C 16-Lead SOIC_N R-16 AD605ARZ-RL1 −40°C to +85°C 16-Lead SOIC_N, 13" Reel R-16 AD605ARZ-RL71 −40°C to +85°C 16-Lead SOIC_N, 7" Reel R-16 AD605BN −40°C to +85°C 16-Lead PDIP N-16 AD605BR −40°C to +85°C 16-Lead SOIC_N R-16 AD605BR-REEL −40°C to +85°C 16-Lead SOIC_N, 13" Reel R-16 AD605BR-REEL7 −40°C to +85°C 16-Lead SOIC_N, 7" Reel R-16 AD605BRZ1 −40°C to +85°C 16-Lead SOIC_N R-16 AD605BRZ-RL1 −40°C to +85°C 16-Lead SOIC_N, 13" Reel R-16 AD605BRZ-RL71 −40°C to +85°C 16-Lead SOIC_N, 7" Reel R-16 AD605-EB Evaluation Board AD605ACHIPS DIE 1 Z = Pb-free part.

Rev. D | Page 20 of 20 NOTES ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C00541-0-1/06(D)