Digitally Controlled VGA. Differential Input and Output. Pin Programmable Low and High Gain Low Range -11 to 17dB

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a    Digitally Controlled VGA

LF to 700MHz  Preliminary Technical Data   AD8370


FEATURES

Differential Input and Output

200 Differential Input 

100 Differential Output

7dB Noise Figure @ Maximum Gain

Two Tone IP3 of 31dBm @ 70MHz

-3dB Bandwidth of 700MHz 

40dB Precision Gain Range

Serial 7-bit Interface

Pin Programmable Low and High Gain Low Range -11 to 17dB

High Range 6 to 34dB Wide Input Dynamic Range

Operation Down to a 3 V Supply

Power Down Feature

APPLICATIONS

Differential ADC Driver IF Sampling Receivers

Cellular/PCS Base Stations RF/IF Gain Stages

SAW Filter Interfacing

Single-Ended to Differential Conversion

GENERAL DESCRIPTION

The AD8370 is a low cost, digitally controlled, variable gain amplifier that provides both high IP3 and low noise figure. The excellent distortion performance and wide bandwidth makes the AD8370 a suitable gain control device for modern receiver designs.

For wide input dynamic range applications the AD8370 provides two input ranges; high-gain and low-gain mode. A vernier 7-bit attenuator provides 28dB of attenuation range with better than 2 dB resolution, and up to 22dB of range with better than 1dB resolution.  The input gain selection allows for an additional 17dB of range FUNCTIONAL BLOCK DIAGRAM

 

and provides for excellent output distortion levels with relatively high input levels.

The AD8370 may be powered on or off by applying the appropriate logic level to the PWUP pin. When powered down the AD8370 consumes less than 5mA and offers excellent input to output isolation. 

REV. PrC  3/12/03                                                                                                                                                                                                                                                        

Fabricated in ADI’s high speed XFCB process, the high bandwidth of the AD8370 provides high frequency and low distortion.  The quiescent current of the AD8370 is 78mA typically.  The AD8370 amplifier comes in a compact 16 pin TSSOP package and will operate over the temperature range of -40°C to +85°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. 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 companies.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700       www.analog.com Fax: 781/326-8703 © 2003 Analog Devices, Inc. All rights reserved.


AD8370-SPECIFICATIONS     (VS=5V, T=25°C, RS=200, RL = 100 at max gain unless otherwise noted)

Parameter

Conditions

Min

Typ

Max

Units

DYNAMIC PERFORMANCE

- 3 dB Bandwidth 

Vout<1 Vp-p 

700

MHz

Bandwidth for 0.1 dB Flatness

Vout<1 Vp-p

TBD

MHz

INPUT STAGE

Maximum Input

Low Gain (1dB Compression)

1.13

Vrms

Maximum Input

High Gain (1dB Compression)

500

mVrms

Input Resistance

Differential, f=10MHz

200

Input Capacitance

Differential, f=10MHz

TBD

pF

Common Mode Input Range

3.2

Vp-p

CMRR

Differential, f=10MHz

60

dB

GAIN CONTROL

INTERFACE (GAIN)

High Gain

Gain Code = 127

34.1

dB

High Gain

Gain Code = 5

6.0

dB

Low Gain

Gain Code = 127

17.1

dB

Low Gain

Gain Code = 5

-11.0

dB

Step Response

For 6 dB Gain Step

10

TBD

ns

OUTPUT STAGE

Output Voltage Swing

RL ≥ 1kΩ (1dB Compression)

8.4

Vp-p

Output Resistance

Differential, f=10MHz

100

Output Capacitance

Differential, f=10MHz

TBD

pF

NOISE/HARMONIC PERFORMANCE

10MHz

Noise Figure

7.2

dB

2nd Harmonic

Vout = 1Vp-p, RL = 100Ω

-75

dBc

3rd Harmonic

Vout = 1Vp-p, RL = 100Ω

-71

dBc

Two-Tone IMD

1Vp-p Composite 

-72

dBc

Output 1dB Compression Point

15.8

dBm

70MHz

Noise Figure

7.4

dB

2nd Harmonic

Vout = 1Vp-p, RL = 100Ω

-68

dBc

3rd Harmonic

Vout = 1Vp-p, RL = 100Ω

-61

dBc

Two-Tone IMD

1Vp-p Composite

-72

dBc

Output 1dB Compression Point

15.8

dBm

140MHz

Noise Figure

7.6

dB

2nd Harmonic

Vout = 1Vp-p, RL = 100Ω

-64

dBc

3rd Harmonic

Vout = 1Vp-p, RL = 100Ω

-52

dBc

Two-Tone IMD

1Vp-p Composite

-69

dBc

Output 1dB Compression Point

14.8

dBm

AD8370-SPECIFICATIONS (VS=5V, T=25°C, RS=200, RL = 100 at max gain unless otherwise noted)

Parameter

Conditions

Min

Typ

Max

Units

NOISE/HARMONIC PERFORMANCE

190MHz

Noise Figure

7.6

dB

2nd Harmonic

Vout = 1Vp-p, RL = 100Ω

-62

dBc

3rd Harmonic

Vout = 1Vp-p, RL = 100Ω

-47

dBc

Two-Tone IMD

1Vp-p Composite

-67

dBc

Output 1dB Compression Point

13.6

dBm

240MHz

Noise Figure

7.7

dB

2nd Harmonic

Vout = 1Vp-p, RL = 100Ω

TBD

dBc

3rd Harmonic

Vout = 1Vp-p, RL = 100Ω

TBD

dBc

Two-Tone IMD

1Vp-p Composite

-65

dBc

Output 1dB Compression Point

13.5

dBm

380MHz

Noise Figure

7.8

dB

2nd Harmonic

Vout = 1Vp-p, RL = 100Ω

TBD

dBc

3rd Harmonic

Vout = 1Vp-p, RL = 100Ω

TBD

dBc

Two-Tone IMD

1Vp-p Composite

-56

dBc

Output 1dB Compression Point

11.2

dBm

POWER INTERFACE

Supply Voltage

2.7

5.5

V

Quiescent Current

PWUP high

78

mA

vs. Temperature

-40°C ≤ TA ≤ 85°C

TBD

TBD

mA

Total Supply Current

PWUP high, Vout = 1Vp-p, RL= 100 Ω

(includes load current)

80

mA

Power Down Current

PWUP low

4

mA

vs. Temperature

-40°C ≤ TA ≤ 85°C

TBD

TBD

mA

POWER DOWN INTERFACE

Power Up Threshold

1.2

V

PWUP Input Bias Current

PWUP = 0 V

135

nA

Notes   

Typical Performance Characteristics (VS = 5V, RS=200, RL=100, T=25°C, unless otherwise noted)

TPC 1. High-Gain Mode AC Response  

TPC 4. Output Third Order Intercept versus

Frequency at Maximum Gain

                                                  Frequency - MHz                                

Frequency - MHz

TPC 2. Low-Gain Mode AC Response                        TPC 5.  Output Compression Point versus Frequency at Maximum Gain


Gain Code TPC 3. Gain versus Gain Code

TPC 6. Noise Figure versus Frequency at Maximum Gain

Basic Connections Figure 1 shows the minimum connections required for basic operation of the AD8370. Supply voltages between 2.7 and 5.5V are allowed. The supply to the VCCO and VCCI pins should be decoupled with at least one low inductance surface-mount ceramic capacitor of 0.1 µF placed as close as possible to the device.  More effective decoupling is provided by placing a 100pF capacitor in parallel and including a ferrite bead in series with the supply.


 

performance when used in an unbalanced environment. 

gain adjustment. The linear voltage gain can be expressed with respect to the gain code as:

A = GainCode Vernier⋅  ⋅(1 (+ PreGain −1)⋅MSB)

where 

Av is the linear voltage gain.

The AD8370 is designed to be a fine gain adjustment variable gain amplifier. The gain control transfer function is linear in voltage gain. On a decibel scale, this results in the exponential transfer functions indicated in TPC 3. At the low end of the gain transfer function, the slope is steep, providing a rather coarse control function. At the higher end of the gain control range the dB step size is decreased allowing for precise


Figure 1. Basic Connections

The AD8370 is designed to be used in differential signal chains. Differential signaling allows for improved evenorder harmonic cancellation and better common-mode immunity than can be achieved using a single-ended design. In order to fully exploit these benefits, it is necessary to drive

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