ANALOG DEVICES AD8375 Service Manual

V

–

Ultralow Distortion IF VGA

FEATURES

Bandwidth of 630 MHz (−3 dB) Gain range: −4 dB to +20 dB Step size: 1 dB ± 0.2 dB Differential input and output Noise figure: 8 dB @ maximum gain Output IP3 of ~50 dBm at 200 MHz Output P1dB of 19 dBm at 200 MHz Provides constant SFDR vs. gain Parallel 5-bit control interface Power-down feature Single 5 V supply operation 24-lead, 4 mm × 4 mm LFCSP

APPLICATIONS

Differential ADC drivers High IF sampling receivers Wideband multichannel receivers Instrumentation

GENERAL DESCRIPTION

The AD8375 is a digitally controlled, variable gain, wide bandwidth amplifier that provides precise gain control, high IP3, and low noise figure. The excellent distortion performance and high signal bandwidth make the AD8375 an excellent gain control device for a variety of receiver applications.

Using an advanced high speed SiGe process and incorporating proprietary distortion cancellation techniques, the AD8375 achieves 50 dBm output IP3 at 200 MHz.

The AD8375 provides a broad 24 dB gain range with 1 dB resolution. The gain is adjusted through a 5-pin control interface and can be driven using standard TTL levels. The open-collector outputs provide a flexible interface, allowing the overall signal gain to be set by the loading impedance. Thus, the signal voltage gain is directly proportional to the load.

The AD8375 is powered on by applying the appropriate logic level to the PWUP pin. The quiescent current of the AD8375 is typically 130 mA. When powered down, the AD8375 consumes less than 5 mA and offers excellent input-to-output isolation.

AD8375

FUNCTIONAL BLOCK DIAGRAM

POS COMM

COM

VIN+

α

VIN–

REGIS TERS

GAIN DECODER

AD8375

POST-AMP

AND

A2A3A4 A1 A0

Figure 1.

Fabricated on an Analog Devices, Inc., high speed SiGe process, the AD8375 is supplied in a compact, thermally enhanced, 4 mm × 4 mm, 24-lead LFCSP package and operates over the temperature range of −40°C to +85°C.

40

–50

–60

–70

–80

–90

–100

HARMONIC DIST ORTIO N (dBc), O UTPUT @ 2V p-p

–110

40 60 80 100 120 140 160 180 200

Figure 2. Harmonic Distortion and Output IP3 vs. Frequency

FREQUENCY (MHz )

OIP3

HD2

HD3

PWUP

OUT+

OUT–

65

60

55

50

45

40

35

30

06724-001

OIP3 (dBm), OUTPUT @ 3dBm/TONE

06724-052

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her 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.

AD8375

REVISION HISTORY

8/07—Revision 0: Initial Version

Basic Structure............................................................................ 12

Applications..................................................................................... 13

Basic Connections...................................................................... 13

Single-Ended-to-Differential Conversion............................... 13

Broadband Operation................................................................ 14

ADC Interfacing......................................................................... 14

Layout Considerations............................................................... 17

Characterization Test Circuits.................................................. 17

Evaluation Board ........................................................................ 18

Outline Dimensions .......................................................................22

Ordering Guide .......................................................................... 22

Rev. 0 | Page 2 of 24

AD8375

SPECIFICATIONS

VS = 5 V, T = 25°C, RS = RL = 150 Ω at 140 MHz, 2 V p-p differential output, unless otherwise noted.

Table 1.

Parameter Conditions Min Typ Max Unit

DYNAMIC PERFORMANCE

−3 dB Bandwidth V Slew Rate 5 V/ns

INPUT STAGE Pin VIN+ and Pin VIN−

Maximum Input Swing For linear operation (AV = −4 dB) 8.5 V p-p Differential Input Resistance Differential 125 150 165 Ω Common-Mode Input Voltage 1.9 V CMRR Gain code = 00000 55 dB

GAIN

Amplifier Transconductance Gain code = 00000 0.060 0.067 0.074 S Maximum Voltage Gain Gain code = 00000 20 dB Minimum Voltage Gain Gain code ≥ 11000 −4 dB Gain Step Size From gain code = 00000 to 11000 0.89 0.98 1.01 dB Gain Flatness All gain codes, 20% fractional bandwidth for fC < 200 MHz 0.12 dB Gain Temperature Sensitivity Gain code = 00000 8 mdB/°C Gain Step Response For VIN = 100 mV p-p, gain code = 10100 to 00000 5 ns

OUTPUT STAGE Pin VOUT+ and Pin VOUT−

Output Voltage Swing At P1dB, gain code = 00000 12.6 V p-p Output Impedance Differential 16||0.8 kΩ||pF

NOISE/HARMONIC PERFORMANCE

46 MHz Gain code = 00000

Noise Figure 8.3 dB Second Harmonic V Third Harmonic V Output IP3 2 MHz spacing, +3 dBm per tone 50 dBm Output 1 dB Compression Point 22 dBm

70 MHz Gain code = 00000

Noise Figure 8.3 dB Second Harmonic V Third Harmonic V Output IP3 2 MHz spacing, 3 dBm per tone 51 dBm Output 1 dB Compression Point 22 dBm

140 MHz Gain code = 00000

Noise Figure 8.3 dB Second Harmonic V Third Harmonic V Output IP3 2 MHz spacing, 3 dBm per tone 51 dBm Output 1 dB Compression Point 20 dBm

200 MHz Gain code = 00000

Noise Figure 8.3 dB Second Harmonic V Third Harmonic V Output IP3 2 MHz spacing, 3 dBm per tone 50 dBm Output 1 dB Compression Point 19 dBm

< 2 V p-p (5.2 dBm) 630 MHz

OUT

= 2 V p-p −92 dBc

OUT

= 2 V p-p −94 dBc

OUT

= 2 V p-p −98 dBc

OUT

= 2 V p-p −95 dBc

OUT

= 2 V p-p −90 dBc

OUT

= 2 V p-p −100 dBc

OUT

= 2 V p-p −85 dBc

OUT

= 2 V p-p −92 dBc

OUT

Rev. 0 | Page 3 of 24

AD8375

Parameter Conditions Min Typ Max Unit

POWER INTERFACE

Supply Voltage 4.5 5.0 5.5 V

VPOS and Output Quiescent Current Thermal connection made to exposed paddle under device 120 125 130 mA

vs. Temperature −40°C ≤ TA ≤ +85°C 150 mA

Power-Down Current PWUP low 2.5 mA

vs. Temperature −40°C ≤TA ≤ +85°C 3 mA

POWER-UP/GAIN CONTROL Pin A0 to Pin A4, Pin PWUP

VIH Minimum voltage for a logic high 1.6 V

VIL Maximum voltage for a logic low 0.8 V

Logic Input Bias Current 900 nA

Table 2. Gain Code vs. Voltage Gain Look-Up Table

5-Bit Binary Gain Code Voltage Gain (dB)

00000 +20 00001 +19 00010 +18 00011 +17 00100 +16 00101 +15 00110 +14 00111 +13 01000 +12 01001 +11 01010 +10 01011 +9 01100 +8

5-Bit Binary Gain Code Voltage Gain (dB)

01101 +7 01110 +6 01111 +5 10000 +4 10001 +3 10010 +2 10011 +1 10100 0 10101 −1 10110 −2 10111 −3 11000 −4 >11000 −4

Rev. 0 | Page 4 of 24

AD8375

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

Supply Voltage, V PWUP, A0 to A4 −0.6 V to (V Input Voltage, V DC Common Mode VCOM ± 0.25 V VCOM ±6 mA Internal Power Dissipation 825 mW θJA (Exposed Paddle Soldered Down) 63.6°C/W θJC (At Exposed Paddle) 14.6°C/W Maximum Junction Temperature 130°C Operating Temperature Range −40°C to +85°C Storage Temperature Range −65°C to +150°C

IN+

POS

, V

IN−

5.5 V + 0.6 V)

POS

−0.15 V to +4.15 V

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

Rev. 0 | Page 5 of 24

AD8375

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

UP

PW

COMM

VPOS

COMM

19

20

21

22

23

24

PIN 1 INDICATOR

1VCOM 2VIN+ 3VIN–

AD8375

4A4

TOP VIEW

5A3

(Not to Scale)

6A2

9

7

8

A0

A1

VPOS

Figure 3. 24-Lead LFCSP

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 VCOM Common-Mode Pin. Typically bypassed to ground using external capacitor. 2 VIN+ Voltage Input Positive. 3 VIN− Voltage Input Negative. 4 A4 MSB for the 5-Bit Gain Control Interface. 5 A3 MSB − 1 for the Gain Control Interface. 6 A2 MSB − 2 for the Gain Control Interface. 7 A1 LSB + 1 for the Gain Control Interface. 8 A0 LSB for the 5-Bit Gain Control Interface. 9, 10, 12, 13, 23 VPOS Positive Supply Pins. Should be bypassed to ground using suitable bypass capacitor. 11, 14, 20, 21, 22, 24 COMM Device Common (DC Ground). 15, 17 VOUT+ Positive Output Pins (Open Collector). Require dc bias of +5 V nominal. 16, 18 VOUT− Negative Output Pins (Open Collector). Require dc bias of +5 V nominal. 19 PWUP Chip Enable Pin. Enabled with a logic high and disabled with a logic low.

18 VOUT– 17 VOUT+ 16 VOUT– 15 VOUT+ 14 COMM 13 VPOS

11

12

10

VPOS

COMM

06724-002

Rev. 0 | Page 6 of 24

AD8375

TYPICAL PERFORMANCE CHARACTERISTICS

VS = 5 V, TA = 25°C, RS = RL = 150 Ω, 2 V p-p output, maximum gain unless otherwise noted.

25

20

15

10

GAIN (dB)

–5

–10

11000010100

46MHz 70MHz 140MHz 200MHz

5

0

–4

5

01111

GAIN CODE

10

01010

15

00101

20

00000

06724-003

Figure 4. Gain vs. Gain Code at 46 MHz, 70 MHz, 140 MHz, and 200 MHz

1.0

0.8

0.6

0.4

0.2

0

–0.2

GAIN ERROR (d B)

–0.4

–0.6

–0.8

–1.0

–4

11000010100

5

01111

GAIN CODE

10

01010

15

00101

Figure 7. Gain Step Error, Frequency 140 MHz

20

10100

06724-006

25

20

15

10

5

GAIN (dB)

0

–5

–10

10 100 1000

FREQUENCY (MHz)

Figure 5. Gain vs. Frequency Response

10

25°C

8

85°C –40°C

6

4

2

0

–2

GAIN ERROR (d B)

–4

–6

–8

–10

–4

11000010100

5

01111

GAIN CODE

10

01010

15

00101

Figure 6. Gain Error over Temperature at 140 MHz

20

00000

20dB 19dB 18dB 17dB 16dB 15dB 14dB 13dB 12dB 11dB 10dB 9dB 8dB 7dB 6dB 5dB 4dB 3dB 2dB 1dB 0dB –1dB –2dB –3dB –4dB

25

INPUT MAX RATING

20

BOUNDARY

200MHz

15

10

OP1dB (dBm)

5

0

06724-004

–4 1 6 11 16 21

GAIN (dB)

140MHz 70MHz 46MHz

06724-007

Figure 8. P1dB vs. Gain at 46 MHz, 70 MHz, 140 MHz, and 200 MHz

25

20

15

10

OP1dB (dBm)

5

0

46 100 150 200 250 300 350 400 450 500

06724-005

FREQUENCY (MHz)

+25°C +85°C –40°C

06724-008

Figure 9. P1dB vs. Frequency at Maximum Gain, Three Temperatures

Rev. 0 | Page 7 of 24

AD8375

–

46MHz 70MHz 140MHz 200MHz

65

60

55

50

OIP3 (dBm)

45

40

35

06724-012

06724-013

52

51

50

49

48

47

46

45

OIP3 (dBm)

44

43

42

41

40

30 50 70 90 110 130 150 170 190 210

AV = +20dB

AV = +10dB

AV = 0dB

AV = –4dB

FREQUENCY (MHz)

Figure 10. Output Third-Order Intercept at Four Gains,

Output Level at 3 dBm/Tone

52

51

50

49

48

47

46

45

OIP3 (dBm)

44

43

42

41

40

–4 –3 –2 –1 0 1 2 3 4 5 6

AV = +20dB

AV = +10dB

P

(dBm)

OUT

AV = 0dB

AV = –4dB

Figure 11. Output Third-Order Intercept vs. Power

at Four Gains, Frequency 140 MHz

55

+25°C 20d B –40°C 20dB +85°C 20d B

50

+25°C 0dB –40°C 0dB +85°C 0dB

45

40

OIP3 (dBm)

35

30

25

06724-009

–3–2–1012345

AV = 20dB

AV = 0dB

P

PER TONE (dBm)

OUT

Figure 13. Output Third-Order Intercept vs. Power,

Frequency 140 MHz, Three Temperatures

70

–75

–80

–85

–90

IMD3 (dBc)

–95

–100

–105

–110

–4 1 6 11 16

06274-010

Figure 14. Two-Tone Output IMD vs. Gain

GAIN (dB)

at 46 MHz, 70 MHz, 140 MHz, and 200 MHz, Output Level at 3 dBm/Tone

70

65

60

55

50

–40°C

OIP3 (dBm)

45

40

35

30

40 60 80 100 120 140 160 18 0 200

+25°C

+85°C

FREQUENCY (MHz)

Figure 12. Output Third-Order Intercept vs. Frequency,

Three Temperatures, Output Level at 3 dBm/Tone

06724-011

Rev. 0 | Page 8 of 24

70

–75

–80

–85

–90

IMD3 (dBc)

–95

–100

–105

–110

40 60 80 100 120 140 160 180 200

+85°C

–40°C

+25°C

FREQUENCY (MHz)

Figure 15. Two-Tone Output IMD vs. Frequency,

Three Temperatures, Output Level at 3 dBm/Tone

06724-014

ANALOG DEVICES AD8375 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

FEATURES

APPLICATIONS

GENERAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAM

TABLE OF CONTENTS

REVISION HISTORY

SPECIFICATIONS

ABSOLUTE MAXIMUM RATINGS

ESD CAUTION

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

TYPICAL PERFORMANCE CHARACTERISTICS