Analog Devices AD604ARS, AD604AN Datasheet

Dual, Ultralow Noise

a

FEATURES
Ultralow Input Noise at Maximum Gain:

0.80 nV/√Hz, 3.0 pA/√Hz

Two 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)

61.0 dB Gain Accuracy
Bandwidth: 40 MHz (–3 dB)
300 kV 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 A/D Converters Directly

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

PAI

PROGRAMMABLE

ULTRALOW NOISE

PREAMPLIFIER

G = 14–20dB

Variable Gain Amplifier

AD604

FUNCTIONAL BLOCK DIAGRAM

PAO

–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

PRODUCT DESCRIPTION

The AD604 is an ultralow noise, very accurate, dual channel,
linear-in-dB variable gain amplifier (VGA) optimized for time­based 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 kΩ 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 seven 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 gain range
of 48 dB which 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 (dB) = (Gain
Scaling (dB/V) × VGN (V)) + (Preamp Gain (dB) – 19 dB).
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 2nd channel’s preamplifier. However, in multiple channel
systems, cascading the AD604 with other devices in the AD60x
VGA family, which 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 provides an input resistance of
approximately 2 MΩ and scale factors from 20 dB/V to
30 dB/V for a V

input voltage of 2.5 V to 1.67 V respect-

REF

ively. 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-pin plastic SSOP, SOIC and DIP,
and is guaranteed for operation over the –40°C to +85°C
temperature range.

REV. 0

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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] World Wide Web Site: http://www.analog.com
Fax: [phone] © Analog Devices, Inc., 1996

AD604–SPECIFICATIONS

(Each Amplifier Channel at TA = +258C, VS = 65 V, RS = 50 V, RL = 500 V, CL = 5 pF, V
range (preamplifier gain = +14 dB), VOCM = 2.5 V, C1 and C2 = 0.1 mF (see Figure 35) unless otherwise noted)

Parameter Conditions Min Typ Max Unit

INPUT CHARACTERISTICS

Preamplifier

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

Preamp Gain = +20 dB ±200 mV

Input Voltage Noise VGN

= 2.9 V, R

= 0 Ω

S

Preamp Gain = +14 dB 0.8 nV/√
Preamp Gain = +20 dB 0.73 nV/√

Input Current Noise Independent of Gain 3.0 pA/√
Noise Figure R

= 50 Ω, f = 1 MHz, VGN = 2.9 V 2.3 dB

S

R

= 200 Ω, f =1 MHz, VGN

S

= 2.9 V 1.1 dB

DSX

Input Resistance 175 Ω
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 Ω, f = 1 MHz, VGN = 2.9 V 8.4 dB

S

R

= 200 Ω, f =1 MHz, VGN

S

= 2.9 V 12 dB

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

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

REF

Hz
Hz
Hz

OUTPUT CHARACTERISTICS

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

≥ 500 Ω 2.5 ± 1.5 V

L

Output Impedance f = 10 MHz 2 Ω
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

3rd 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 #1: VGN = 2.65 V, Inputs Shorted –30 dB
Ch #2: VGN = 1.5 V (Mid Gain) dB

Group Delay Variation 1 MHz < f < 10 MHz, Full Gain Range ±2ns
V

Input Resistance 45 kΩ

OCM

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 V
Output Offset Variation V

= 2.500 V, V

REF

= 2.500 V, V

REF

= 2.500 V –50 ±30 +50 mV

OCM

= 2.500 V 30 50 mV

OCM

–2–

REV. 0

AD604

WARNING!

ESD SENSITIVE DEVICE

Parameter Conditions Min Typ Max Unit

GAIN CONTROL INTERFACE

Gain Scaling Factor V

Gain Range Preamp Gain = +14 dB 0 to +48 dB

Input Voltage (VGN) Range 20 dB/V, V
Input Bias Current –0.4 µA
Input Resistance 2MΩ
Response Time 48 dB Gain Change 0.2 µs
V

Input Resistance 10 kΩ

REF

POWER SUPPLY

Specified Operating Range One Complete Channel ±5V

Power Dissipation One Complete Channel 220 mW

Quiescent Supply Current VPOS, One Complete Channel 32 36 mA

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

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

= 2.5 V, 0.4 V < VGN < 2.4 V 19 20 21 dB/V

REF

= 1.67 V 30 dB/V

V

REF

Preamp Gain = +20 dB +6 to +54 dB

= 2.5 V 0.1 to 2.9 V

REF

One DSX Only +5 V

One DSX Only 95 mW

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

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

= 2 V p-p 0.6 µs

OUT

ABSOLUTE MAXIMUM RATINGS

Supply Voltage ±V

S

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

Internal Power Dissipation

Plastic (N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 W

Model Range u

AD604AN –40°C to +85°C57°C/W N-24
AD604AR –40°C to +85°C70°C/W R-24
AD604ARS –40°C to +85°C 112°C/W R-24

*N = Plastic DIP, R = Small Outline IC (SOIC), RS = Shrink Small Outline

Package (SSOP).

ORDERING GUIDE

Temperature Package

Small Outline (R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 W

Shrink Small Outline (RS) . . . . . . . . . . . . . . . . . . . . . 1.1 W

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

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

Lead Temperature, Soldering 60 seconds . . . . . . . . . +300°C

NOTES

1

Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and 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 and 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.

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.

JA

Option*

REV. 0

–3–

AD604

PIN DESCRIPTIONS

Pin No. Mnemonic Description

Pin 1 –DSX1 CH1 Negative Signal Input to DSX1.
Pin 2 +DSX1 CH1 Positive Signal Input to DSX1.
Pin 3 PAO1 CH1 Preamplifier Output.
Pin 4 FBK1 CH1 Preamplifier Feedback Pin.
Pin 5 PAI1 CH1 Preamplifier Positive Input.
Pin 6 COM1 CH1 Signal Ground; when connected to positive supply, Preamplifier1 will shut down.
Pin 7 COM2 CH2 Signal Ground; when connected to positive supply, Preamplifier2 will shut down.
Pin 8 PAI2 CH2 Preamplifier Positive Input.
Pin 9 FBK2 CH2 Preamplifier Feedback Pin.
Pin 10 PAO2 CH2 Preamplifier Output.
Pin 11 +DSX2 CH2 Positive Signal Input to DSX2.
Pin 12 –DSX2 CH2 Negative Signal Input to DSX2.
Pin 13 VGN2 CH2 Gain-Control Input and Power-Down Pin. If grounded, device is off,

otherwise positive voltage increases gain.
Pin 14 VOCM Input to this pin defines common-mode of output at OUT1 and OUT2.
Pin 15 OUT2 CH2 Signal Output.
Pin 16 GND2 Ground.
Pin 17 VPOS Positive Supply.
Pin 18 VNEG Negative Supply.
Pin 19 VNEG Negative Supply.
Pin 20 VPOS Positive Supply.
Pin 21 GND1 Ground.
Pin 22 OUT1 CH1 Signal Output.
Pin 23 VREF Input to this pin sets gain-scaling for both channels +2.5 V = 20 dB/V, +1.67 V = 30 dB/V.
Pin 24 VGN1 CH1 Gain-Control Input and Power-Down Pin. If grounded, device is off;

otherwise positive voltage increases gain.

PIN CONFIGURATION

1

–DSX1
+DSX1

PAO1

FBK1

PAI1
COM1
COM2

PAI2

FBK2

PAO2
+DSX2
–DSX2

2
3
4
5

AD604

6

TOP VIEW

(Not to Scale)

7

8

9
10
11
12

24

VGN1
VREF

23

OUT1

22

GND1

21
20

VPOS

19

VNEG

18

VNEG

17

VPOS
GND2

16
15

OUT2

14

VOCM

13

VGN2

–4–

REV. 0

Typical Performance Characteristics (per Channel)–AD604

VGN – Volts

50

20

–10

0.1 2.9

40

30

10

0

0.5 0.9 1.3 1.7 2.1 2.5

ACTUAL

ACTUAL

30dB/V

VREF = 1.67V

20dB/V
VREF

= 2.50V

GAIN – dB

VGN – Volts

GAIN ERROR – dB

2.0

0.2

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

0.7 1.2 1.7 2.2 2.7

FREQ = 5MHz

FREQ = 10MHz

FREQ = 1MHz

DELTA GAIN – dB

PERCENTAGE

25

–1.0

20

15

10

5

0

–0.8

–0.6 –0.4 –0.2

0.1 0.3 0.5

0.7

0.9

∆G(dB) =
G(CH1) – G(CH2)

VGN1 = 2.50V
VGN2 = 2.50V

N = 50

(Unless otherwise noted G (preamp) = +14 dB, V

50

40

3 CURVES

– Volts

–40°C,
+25°C,
+85°C

30

20

GAIN – dB

10

0

–10

0.1 2.9

0.5 0.9 1.3 1.7 2.1 2.5
VGN – Volts

Figure 1. Gain vs. VGN

40

37.5

35

32.5

30

27.5

GAIN SCALING – dB/V

25

22.5

20

1.25

THEORETICAL

ACTUAL

1.5 1.75 2 2.25 2.5
V

REF

= 2.5 V (20 dB/V Scaling), f = 1 MHz, RL = 500 V, CL = 5 pF, TA = +258C, VSS = 65V)

REF

60

50

40

30

20

GAIN – dB

10

0

–10

–20

0.1

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

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 – Volts

–40°C

+25°C

+85°C

0.7 1.2 1.7 2.2 2.7
VGN – Volts

Figure 3. Gain vs. VGN for Different
Gain Scalings

Figure 4. Gain Scaling vs. V

2.0

1.5

1.0

0.5

0

–0.5

GAIN ERROR – dB

–1.0

–1.5

–2.0

0.2

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

REV. 0

VREF = 1.67V

0.7 1.2 1.7 2.2 2.7

30dB/V

VGN – Volts

REF

20dB/V

VREF = 2.50V

Figure 5. Gain Error vs. VGN at
Different Temperatures

25

20

15

10

PERCENTAGE

5

0

–0.6

–1.0

–0.8

–0.4 –0.2 0.1 0.3 0.5 0.7 0.9

DELTA GAIN – dB

N = 50
VGN1 = 1.0V
VGN2 = 1.0V
∆G(dB) =
G(CH1) – G(CH2)

Figure 8. Gain Match; VGN1 = VGN2 =

1.0 V

–5–

Figure 6. Gain Error vs. VGN at
Different Frequencies

Figure 9. Gain Match: VGN1 = VGN2 =

2.50 V

AD604–Typical Performance Characteristics (per Channel)

VGN – Volts

210

0.1

190

170

150

130

110

90

0.5 0.9 1.3 1.7 2.1 2.5 2.9

+85°C

+25°C

–40°C

NOISE – n V / √Hz

NOISE – p V / √Hz

FREQUENCY – Hz

770

745

740

760

765

750

755

100k 1M 10M

VGN = 2.9V

VGN – Volts

dB

40

20

0

0

1.2

35

30

25

15

10

5

0.4 0.8 1.6 2.0 2.4 2.8

RS = 240Ω

(Unless otherwise noted G (preamp) = +14 dB, V

= 2.5 V (20 dB/V Scaling), f = 1 MHz, RL = 500 V, CL = 5 pF, TA = +258C, VSS = 65V)

REF

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 – n V / √Hz

1

2.55

2.54

2.53

2.52

2.51

2.50

– Volts

OUT

2.49

V

2.48

2.47

2.46

2.45

VOCM = 2.50V

+85°C

0.2

0.7 1.2 1.7 2.2 2.7

–40°C

+25°C

VGN – Volts

Figure 11. Output Offset vs. VN

900

VGN = 2.9V

850

800

750

700

NOISE – p V / √Hz

650

Figure 12. Output Referred Noise vs.
VGN

0.1

0.1 2.9

0.5 0.9 1.3 1.7 2.1 2.5
VGN – Volts

Figure 13. Input Referred Noise vs.
VGN

10

VGN = 2.9V

1

NOISE – n V / √Hz

0.1
1101k100

Figure 16. Input Referred Noise vs.
R

SOURCE

R

R

SOURCE

SOURCE

– Ω

ALONE

600

–40 –20 20 40 60

080

TEMPERATURE – °C

Figure 14. Input Referred Noise vs.
Temperature

16
15
14
13
12
11
10

9

dB

8
7
6
5

4

3
2
1

110

Figure 17. Noise Figure vs. R

VGN = 2.9V

100
RIN

1k

10k

SOURCE

90

Figure 15. Input Referred Noise vs.
Frequency

Figure 18. Noise Figure vs. VGN

REV. 0–6–