Analog Devices AD604 a Datasheet

Dual, Ultralow Noise

Variable Gain Amplifier

AD604

FEATURES
Ultralow Input Noise at Maximum Gain:

0.80 nV/÷Hz, 3.0 pA/÷Hz

2 Independent Linear-in-dB Channels
Absolute Gain Range per Channel Programmable:

0 dB to 48 dB (Preamp Gain = 14 dB), through

6 dB to 54 dB (Preamp Gain = 20 dB)
1.0 dB Gain Accuracy
Bandwidth: 40 MHz (–3 dB)
300 k Input Resistance
Variable Gain Scaling: 20 dB/V through 40 dB/V
Stable Gain with Temperature and Supply Variations
Single-Ended Unipolar Gain Control
Power Shutdown at Lower End of Gain Control
Can Drive ADCs Directly

APPLICATIONS
Ultrasound and Sonar Time-Gain Control
High Performance AGC Systems
Signal Measurement

PRODUCT DESCRIPTION

The AD604 is an ultralow noise, very accurate, dual-channel,
linear-in-dB variable gain amplifier (VGA) optimized for time
based variable gain control in ultrasound applications; however,
it will support any application requiring low noise, wide band­width, variable gain control. Each channel of the AD604 provides
a 300 kW input resistance and unipolar gain control for ease of
use. User determined gain ranges, gain scaling (dB/V), and dc
level shifting of output further optimize application performance.

Each channel of the AD604 utilizes a high performance pre­amplifier that provides an input referred noise voltage of

0.8 nV/÷Hz. The very accurate linear-in-dB response of the
AD604 is achieved with the differential input exponential amplifier
(DSX-AMP) architecture. Each of the DSX-AMPs comprise a
variable attenuator of 0 dB to 48.36 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 48.36 dB for the ladder network.

Each independent channel of the AD604 provides a 48 dB gain
range that can be optimized for the application by programming
the preamplifier with a single external resistor in the preamp
feedback path. The linear-in-dB gain response of the AD604
can be described by the equation

G Gain Scaling / VGN

dB dB V V

=

()

()

Preamp Gain

+

()

()¥()

dB dB

– 19

()

FUNCTIONAL BLOCK DIAGRAM

–DSX

LADDER NETWORK

PRECISION PASSIVE
INPUT ATTENUATOR

+DSX

DIFFERENTIAL

ATTENUATOR

R-1.5R

0 TO –48.4dB

VGN

GAIN CONTROL

AND SCALING

AFA

FIXED GAIN

AMPLIFIER

34.4dB

VREF

OUT

VOCM

PAI

PROGRAMMABLE

ULTRALOW NOISE

PREAMPLIFIER
G = 14dB–20dB

PAO

Preamplifier gains between 5 and 10 (14 dB and 20 dB) provide
overall gain ranges per channel of 0 dB through 48 dB and 6 dB
through 54 dB. The two channels of the AD604 can be cascaded
to provide greater levels of gain range by bypassing the second
channel’s preamplifier. However, in multiple channel systems,
cascading the AD604 with other devices in the AD60x VGA
family that do not include a preamplifier may provide a more
efficient solution. The AD604 provides access to the output of
the preamplifier, allowing for external filtering between the
preamplifier and the differential attenuator stage.

The gain control interface of the AD604 provides an input
resistance of approximately 2 MW 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
linear-in-dB with control voltages of 0.4 V to 2.4 V with the
20 dB/V scale. Below and above this gain control range, the gain
begins to deviate from the ideal linear-in-dB control law. The
gain control region below 0.1 V is not used for gain control. In
fact when the gain control voltage is <50 mV, the amplifier
channel is powered down to 1.9 mA.

The AD604 is available in a 24-lead SSOP, SOIC, and PDIP
package and is guaranteed for operation over the –40∞C to +85∞C
temperature range.

REV. A

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. 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: [phone] www.analog.com
Fax: [phone] © 2004 Analog Devices, Inc. All rights reserved.

AD604–SPECIFICATIONS

Each Amplifier Channel at TA = 25C, VS = 5 V, RS = 50 , RL = 500 , CL = 5 pF, V
range (preamplifier gain = 14 dB), VOCM = 2.5 V, C1 and C2 = 0.1 F (see Figure 35), unless otherwise noted.

Parameter Conditions Min Typ Max Unit

INPUT CHARACTERISTICS

Preamplifier

Input Resistance 300 kW
Input Capacitance 8.5 pF
Input Bias Current –27 mA
Peak Input Voltage Preamp Gain = 14 dB ± 400 mV

Preamp Gain = 20 dB ± 200 mV

Input Voltage Noise VGN

= 2.9 V, RS = 0 W

Preamp Gain = 14 dB 0.8 nV/÷Hz
Preamp Gain = 20 dB 0.73 nV/÷Hz

Input Current Noise Independent of Gain 3.0 pA/÷Hz
Noise Figure R

= 50 W, f = 10 MHz, VGN = 2.9 V 2.3 dB

S

= 200 W, f =10 MHz, VGN = 2.9 V 1.1 dB

R

S

DSX

Input Resistance 175 W
Input Capacitance 3.0 pF
Peak Input Voltage 2.5 ± 2V
Input Voltage Noise VGN
Input Current Noise VGN
Noise Figure R

= 2.9 V 1.8 nV/÷Hz
= 2.9 V 2.7 pA/÷Hz

= 50 W, f = 10 MHz, VGN = 2.9 V 8.4 dB

S

= 200 W, f =10 MHz, VGN = 2.9 V 12 dB

R

S

Common-Mode Rejection Ratio f = 1 MHz, VGN = 2.65 V –20 dB

OUTPUT CHARACTERISTICS

–3 dB Bandwidth Constant with Gain 40 MHz
Slew Rate VGN = 1.5 V, Output = 1 V Step 170 V/ms
Output Signal Range R

≥ 500 W 2.5 ± 1.5 V

L

Output Impedance f = 10 MHz 2 W
Output Short-Circuit Current ± 40 mA
Harmonic Distortion VGN

= 1 V, V

OUT

= 1 V p-p
HD2 f = 1 MHz –54 dBc
HD3 f = 1 MHz –67 dBc
HD2 f = 10 MHz –43 dBc
HD3 f = 10 MHz –48 dBc

Two-Tone Intermodulation VGN = 2.9 V, V

= 1 V p-p

OUT

Distortion (IMD) f = 1 MHz –74 dBc

f = 10 MHz –71 dBc

Third-Order Intercept f = 10 MHz, VGN

V

= 1 V p-p, Input Referred

OUT

1 dB Compression Point f = 1 MHz, VGN
Channel-to-Channel Crosstalk V

= 1 V p-p, f = 1 MHz

OUT

= 2.65 V, –12.5 dBm

= 2.9 V, Output Referred 15 dBm

Ch No. 1: VGN = 2.65 V, Inputs Shorted –30 dB
Ch No. 2: VGN = 1.5 V (Mid Gain) dB

Group Delay Variation 1 MHz < f < 10 MHz, Full Gain Range ± 2ns
VOCM Input Resistance 45 kW

ACCURACY

Absolute Gain Error

0 dB to 3 dB 0.25 V < VGN < 0.400 V –1.2 +0.75 +3 dB

3 dB to 43 dB 0.400 V < VGN < 2.400 V –1.0 ± 0.3 +1.0 dB

43 dB to 48 dB 2.400 V < VGN < 2.65 V –3.5 –1.25 +1.2 dB

Gain Scaling Error 0.400 V < VGN < 2.400 V ±0.25 dB/V
Output Offset Voltage VREF = 2.500 V, VOCM = 2.500 V –50 ± 30 +50 mV
Output Offset Variation VREF = 2.500 V, VOCM = 2.500 V 30 50 mV

= 2.50 V (Scaling = 20 dB/V), 0 dB to 48 dB gain

REF

REV. A–2–

AD604

SPECIFICATIONS

Parameter Conditions Min Typ Max Unit

GAIN CONTROL INTERFACE

Gain Scaling Factor VREF = 2.5 V, 0.4 V < VGN < 2.4 V 19 20 21 dB/V

VREF = 1.67 V 30 dB/V

Gain Range Preamp Gain = 14 dB 0 to 48 dB

Preamp Gain = 20 dB 6 to 54 dB

Input Voltage (VGN) Range 20 dB/V, VREF = 2.5 V 0.1 to 2.9 V
Input Bias Current –0.4 mA
Input Resistance 2MW
Response Time 48 dB Gain Change 0.2 ms
VREF Input Resistance 10 kW

POWER SUPPLY

Specified Operating Range One Complete Channel ± 5V

One DSX Only 5 V

Power Dissipation One Complete Channel 220 mW

One DSX Only 95 mW

Quiescent Supply Current VPOS, One Complete Channel 32 36 mA

VPOS, One DSX Only 19 23 mA
VNEG, One Preamplifier Only –15 –12 mA

Powered Down VPOS, VGN < 50 mV, One Channel 1.9 3.0 mA

VNEG, VGN < 50 mV, One Channel –150 mA

Power-Up Response Time 48 dB Gain Change, V
Power-Down Response Time 0.4 ms

= 2 V p-p 0.6 ms

OUT

ABSOLUTE MAXIMUM RATINGS

Supply Voltage ± V

S

1, 2, 3

Pins 17, 18, 19, 20 (with Pins 16, 22 = 0 V) . . . . . . ± 6.5 V

Input Voltages

Pins 1, 2, 11, 12 . . . . . . . . . . . . . VPOS/2 ± 2 V Continuous

Pins 4, 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 2 V

Pins 5, 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VPOS, VNEG

Pins 6, 7, 13, 14, 23, 24 . . . . . . . . . . . . . . . . . . . . . VPOS, 0

NOTES

1

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.

2

Pins 1, 2, 11, 12, 13, 14, 23, 24 are part of a single-supply circuit. The part will most

likely be damaged if any of these pins are accidentally connected to VN.

3

When driven from an external low impedance source.

4

Using MIL STD 883 test method G43-87 with a 1S (2-layer) test board.

Internal Power Dissipation

PDIP (N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 W

SOIC (R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 W

SSOP (RS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 W

Operating Temperature Range . . . . . . . . . . . –40∞C to +85∞C

Storage Temperature Range . . . . . . . . . . . . –65∞C to +150∞C

Lead Temperature, Soldering 60 sec . . . . . . . . . . . . . . . 300∞C

4

␪

JA

AD604AN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105∞C

AD604AR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73∞C

AD604ARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112∞C

4

␪

JC

AD604AN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35∞C

Model Range Option Description

AD604AN –40∞C to +85∞C N-24 PDIP
AD604AR –40∞C to +85∞C R-24 SOIC
AD604AR-REEL –40∞C to +85∞C R-24 SOIC
AD604ARS –40∞C to +85∞C RS-24 SSOP
AD604ARS-REEL –40∞C to +85∞C RS-24 SSOP
AD604ARS-REEL7 –40∞C to +85∞C RS-24 SSOP
AD604-EB

ORDERING GUIDE

Temperature Package

AD604AR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38∞C

AD604ARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34∞C

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD604 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.

Evaluation Board

WARNING!

ESD SENSITIVE DEVICE

REV. A

–3–

AD604

PIN CONFIGURATION

–DSX1

1

2

+DSX1

3

PAO1

4

FBK1

5

PAI1

COM1

COM2

PAI2

FBK2

PAO2

+DSX2

–DSX2

AD604

6

TOP VIEW

(Not to Scale)

7

8

9

10

11

12

PIN FUNCTION DESCRIPTIONS

Pin No. Mnemonic Description

1 –DSX1 CH1 Negative Signal Input to DSX1.

2 +DSX1 CH1 Positive Signal Input to DSX1.

3 PAO1 CH1 Preamplifier Output.

4 FBK1 CH1 Preamplifier Feedback Pin.

5 PAI1 CH1 Preamplifier Positive Input.

6 COM1 CH1 Signal Ground. When connected to positive supply, Preamplifier 1 will shut down.

7 COM2 CH2 Signal Ground. When connected to positive supply, Preamplifier 2 will shut down.

8 PAI2 CH2 Preamplifier Positive Input.

9 FBK2 CH2 Preamplifier Feedback Pin.

10 PAO2 CH2 Preamplifier Output.

11 +DSX2 CH2 Positive Signal Input to DSX2.

12 –DSX2 CH2 Negative Signal Input to DSX2.

13 VGN2 CH2 Gain-Control Input and Power-Down Pin. If grounded, device is off;

otherwise, positive voltage increases gain.

14 VOCM Input to this pin defines the common-mode of the output at OUT1 and OUT2.

15 OUT2 CH2 Signal Output.

16 GND2 Ground.

17 VPOS Positive Supply.

18 VNEG Negative Supply.

19 VNEG Negative Supply.

20 VPOS Positive Supply.

21 GND1 Ground.

22 OUT1 CH1 Signal Output.

23 VREF Input to this pin sets gain-scaling for both channels to 2.5 V = 20 dB/V, 1.67 V = 30 dB/V.

24 VGN1 CH1 Gain-Control Input and Power-Down Pin. If grounded, the device is off;

otherwise, positive voltage increases gain.

VGN1

24

23

VREF

22

OUT1

GND1

21

VPOS

20

VNEG

19

VNEG

18

VPOS

17

16

GND2

15

OUT2

14

VOCM

13

VGN2

REV. A–4–

Typical Performance Characteristics–AD604

Unless otherwise noted, G (preamp) = 14 dB, VREF = 2.5 V (20 dB/V Scaling), f = 1 MHz, RL = 500 , CL = 5 pF, TA = 25C, VSS = 5V

50

40

30

20

GAIN (dB)

10

0

–10

0.5 0.9 1.3 1.7 2.1 2.5

0.1 2.9
VGN (V)

Figure 1. Gain vs. VGN for
Three Temperatures

40.0

37.5

35.0

32.5

30.0

27.5

25.0

GAIN SCALING (dB/V)

22.5

20.0

1.25

THEORETICAL

ACTUAL

1.50 1.75 2.00 2.25 2.50
VREF (V)

Figure 4. Gain Scaling vs. VREF

3 CURVES

–40C,
+25C,

+85C

60

50

40

30

20

GAIN (dB)

10

0

–10

–20

0.1

G (PREAMP) = +14dB
(0dB – +48dB)

G (PREAMP) = +20dB
(+6dB – +54dB)

DSX ONLY

(–14dB – +34dB)

0.5 0.9 1.3 1.7 2.1 2.5 2.9
VGN (V)

Figure 2. Gain vs. VGN for
Different Preamp Gains

2.0

1.5

1.0

0.5

0

–0.5

GAIN ERROR (dB)

–1.0

–1.5

–2.0

0.2

0.7 1.2 1.7 2.2 2.7

–40C

+85C

VGN (V)

Figure 5. Gain Error vs. VGN
at Different Temperatures

+25C

50

40

30dB/V

VREF = 1.67V

30

20

GAIN (dB)

10

0

–10

0.1 2.9

0.5 0.9 1.3 1.7 2.1 2.5

ACTUAL

V20dB/

VREF = 2.50V

VGN (V)

Figure 3. Gain vs. VGN for
Different Gain Scalings

2.0

1.5

1.0

0.5

–0.5

GAIN ERROR (dB)

–1.0

–1.5

–2.0

FREQ = 1MHz

0

FREQ = 10MHz

0.2

0.7 1.2 1.7 2.2 2.7
VGN (V)

FREQ = 5MHz

Figure 6. Gain Error vs. VGN
at Different Frequencies

ACTUAL

2.0

1.5

1.0

0.5

0

–0.5

GAIN ERROR (dB)

–1.0

–1.5

–2.0

0.2

30dB/V

VREF = 1.67V

0.7 1.2 1.7 2.2 2.7
VGN (V)

Figure 7. Gain Error vs. VGN
for Different Gain Scalings

REV. A

20dB/V

VREF = 2.50V

25

20

15

10

PERCENTAGE

5

0

–0.8 –0.6 –0.4 –0.2 0.1 0.3 0.5 0.7 0.9

–1.0

DELTA GAIN (dB)

Figure 8. Gain Match;
VGN1 = VGN2 = 1.0 V

–5–

N = 50
VGN1 = 1.0V
VGN2 = 1.0V

G(dB) =
G(CH1) – G(CH2)

25

20

15

10

PERCENTAGE

5

0

–1.0

–0.8 –0.6–0.4 –0.2 0.1 0.3 0.5 0.7 0.9

DELTA GAIN (dB)

Figure 9. Gain Match:
VGN1 = VGN2 = 2.50 V

N = 50
VGN1 = 2.50V
VGN2 = 2.50V
G(dB) =

G(CH1) – G(CH2)

AD604

k

k

50

VGN = 2.5V

40

30

20

10

0

GAIN (dB)

–10

–20

–30

–40

–50

100k

VGN = 1.5V

VGN = 0.5V

VGN = 0.1V

VGN = 0.0V

VGN = 2.9V

1M 10M 100M
FREQUENCY (Hz)

Figure 10. AC Response

1000

100

10

NOISE (nV/ Hz)

1

2.55

VOCM = 2.50V

2.54

2.53

2.52

2.51

(V)

2.50

OUT

2.49

V

2.48

2.47

2.46

2.45

0.2

+85C

0.7 1.2
VGN (V)

–40C

+25C

1.7

2.2 2.7

Figure 11. Output Offset vs. VGN

900

VGN = 2.9V

850

800

750

700

NOISE (pV/ Hz

650

210

190

170

150

NOISE (nV/ Hz)

130

110

90

0.5 0.9 1.3 1.7 2.1 2.5 2.9

0.1

+85C

+25C

VGN (V)

Figure 12. Output Referred
Noise vs. VGN

770

VGN = 2.9V

765

760

755

NOISE (pV/ Hz)

750

745

–40C

0.1

0.1 2.9

0.5 0.9 1.3 1.7 2.1 2.5
VGN (V)

Figure 13. Input Referred
Noise vs. VGN

10

VGN = 2.9V

1

NOISE (nV/ Hz)

R

ALONE

SOURCE

0.1
110

R

SOURCE

()

100

Figure 16. Input Referred
Noise vs. R

SOURCE

600

–40 –20 20 40 60

0

TEMPERATURE (C)

90

80

Figure 14. Input Referred
Noise vs. Temperature

16
15
14
13
12
11
10

9

dB

8
7
6
5
4
3
2

1

1

10

1

Figure 17. Noise Figure vs. R

100

R

SOURCE

VGN = 2.9V

1k

10

SOURCE

740

100k 1M 10M

FREQUENCY (Hz)

Figure 15. Input Referred
Noise vs. Frequency

40

35

30

25

20

dB

15

10

5

0

0.4 0.8 1.6 2.0 2.4 2.8

0

1.2
VGN (V)

RS = 240

Figure 18. Noise Figure vs. VGN

REV. A–6–