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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

200Ω Differential Input

100Ω 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.

AD8370-SPECIFICATIONS (V_S=5V, T=25°C, R_S=200Ω, R_L = 100Ω 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		Ω
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		Ω
Output Capacitance	Differential, f=10MHz		TBD		pF
NOISE/HARMONIC PERFORMANCE 10MHz Noise Figure			7.2		dB
2^nd Harmonic	Vout = 1Vp-p, RL = 100Ω		-75		dBc
3^rd 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
2^nd Harmonic	Vout = 1Vp-p, RL = 100Ω		-68		dBc
3^rd 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
2^nd Harmonic	Vout = 1Vp-p, RL = 100Ω		-64		dBc
3^rd 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 (V_S=5V, T=25°C, R_S=200Ω, R_L = 100Ω at max gain unless otherwise noted)

Parameter	Conditions	Min	Typ	Max	Units
NOISE/HARMONIC PERFORMANCE 190MHz Noise Figure			7.6		dB
2^nd Harmonic	Vout = 1Vp-p, RL = 100Ω		-62		dBc
3^rd 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
2^nd Harmonic	Vout = 1Vp-p, RL = 100Ω		TBD		dBc
3^rd 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
2^nd Harmonic	Vout = 1Vp-p, RL = 100Ω		TBD		dBc
3^rd 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 ≤ T_A ≤ 85°C	TBD		TBD	mA
Total Supply Current	PWUP high, Vout = 1Vp-p, R_L= 100 Ω (includes load current)		80		mA
Power Down Current	PWUP low		4		mA
vs. Temperature	-40°C ≤ T_A ≤ 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=200Ω, RL=100Ω, 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

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