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LTC6412

6412fa

TYPICAL APPLICATION

DESCRIPTION

800MHz, 31dB Range

Analog-Controlled VGA

The LTC

6412 is a fully differential variable gain ampliﬁ er

with linear-in-dB analog gain control. It is designed for

AC-coupled operation in IF receiver chains from 1MHz

to 500MHz. The part has a constant OIP3 across a wide

output amplitude range and across the 31dB gain control

range. The output noise (NF + Gain) is also ﬂ at versus gain

to provide a uniform spurious-free dynamic range (SFDR)

>120dB over the full gain control range at 240MHz.

The LTC6412 is ideal for interfacing with the LT

5527 and

LT5557 downconverting mixers, LTC6410-6 IF ampliﬁ er

and the LTC6400/LTC6401/LTC6416 ADC drivers for use

in 12-, 14-, and 16-bit ADC applications.

The LTC6412 recovers quickly from an overdrive condition,

and the EN pin allows for a fast output signal disable to

protect sensitive downstream components. Asserting the

SHDN pin reduces the current consumption below 1mA

for power-down or sleep modes.

3.3V Fully Differential 240MHz IF Receiver Chain with 31dB Gain Control

FEATURES

APPLICATIONS

800MHz –3dB Small-Signal Bandwidth

Continuously-Adjustable Gain Control

–14dB to +17dB Linear-in-dB Gain Range

35dBm OIP3 at 240MHz Across All Gain Settings

10dB Noise Figure at Maximum Gain

(IIP3 – NF) = +8dBm at 240MHz Across All Gains

2.7nV/√Hz Input Referred Noise

Differential Inputs and Outputs

50Ω Input Impedance Across all Gains

Single Supply Operation from 3V to 3.6V

110mA Supply Current

4mm × 4mm × 0.75mm 24-Pin QFN Package

IF Signal Chain Automatic Gain Control (AGC)

2.5G and 3G Cellular Basestation Transceivers

WiMAX, WiBro, WLAN Receivers

Satellite and GPS Receiver IF

SHDN

GND

REF

DECL1

DECL2

–V

+IN

10nF

0.1μF

BPF

GND

6412 TA01

LTC2208

0.1μF

3.3V

1nF

0.1μF

180nH180nH

3.3V

+OUT

–OUT

–

–OUT

+OUT

10nF

0.1μF

GAIN CONTROL

(+ SLOPE MODE)

IF INPUT

+IN

–

LTC6400-8

–IN

LTC6412

–IN

2.2μF

VGA Gain vs Frequency

Over Gain Control Range

FREQUENCY (MHz)

–20

GAIN (dB)

–10

1 100 1000 10000

6412 G01

–30

MAX

MIN

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Summary of content (24 pages)

PAGE 1
LTC6412 800MHz, 31dB Range Analog-Controlled VGA FEATURES DESCRIPTION n The LTC®6412 is a fully differential variable gain ampliﬁer with linear-in-dB analog gain control. It is designed for AC-coupled operation in IF receiver chains from 1MHz to 500MHz. The part has a constant OIP3 across a wide output amplitude range and across the 31dB gain control range.
PAGE 2
LTC6412 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Total Supply Voltage (VCC to GND)...........................3.8V Ampliﬁer Input Current (+IN, –IN)........................±20mA Ampliﬁer Output Current (+OUT, –OUT) ...............±70mA Input Current (+VG, –VG, VREF, EN, SHDN ) .........±10mA Input Current (VCM, DECL1, DECL2) ....................±10mA RF Input Power, Continuous, 50Ω......................+15dBm RF Input Power, 100μs pulse, 50Ω ....................
PAGE 3
LTC6412 DC ELECTRICAL CHARACTERISTICS The l denotes speciﬁcations that apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. DC electrical performance measured using DC test circuit schematic. VIN(DIFF) is deﬁned as (+IN) – (–IN). VOUT(DIFF) is deﬁned as (+OUT) – (–OUT). VIN(CM) is deﬁned as [(+IN) + (–IN)]/2. VOUT(CM) is deﬁned as [(+OUT) + (–OUT)]/2. Unless noted otherwise, default operating conditions are VCC = 3.3V, EN = 0.8V, SHDN = 2.
PAGE 4
LTC6412 DC ELECTRICAL CHARACTERISTICS The l denotes speciﬁcations that apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. DC electrical performance measured using DC test circuit schematic. VIN(DIFF) is deﬁned as (+IN) – (–IN). VOUT(DIFF) is deﬁned as (+OUT) – (–OUT). VIN(CM) is deﬁned as [(+IN) + (–IN)]/2. VOUT(CM) is deﬁned as [(+OUT) + (–OUT)]/2. Unless noted otherwise, default operating conditions are VCC = 3.3V, EN = 0.8V, SHDN = 2.
PAGE 5
LTC6412 AC ELECTRICAL CHARACTERISTICS The l denotes speciﬁcations that apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. Typical AC electrical performance measured in demo board DC1464A (Figure 3, Test Circuit A) unless otherwise noted. Default operating conditions are VCC = 3.3V, EN = 0.8V, SHDN = 2.2V, +VG tied to VREF (negative gain slope mode), and ZSOURCE = ZLOAD = 50Ω unless otherwise noted.
PAGE 6
LTC6412 AC ELECTRICAL CHARACTERISTICS The l denotes speciﬁcations that apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. Typical AC electrical performance measured in demo board DC1464A (Figure 3, Test Circuit A) unless otherwise noted. Default operating conditions are VCC = 3.3V, EN = 0.8V, SHDN = 2.2V, +VG tied to VREF (negative gain slope mode), and ZSOURCE = ZLOAD = 50Ω unless otherwise noted.
PAGE 7
LTC6412 AC ELECTRICAL CHARACTERISTICS The l denotes speciﬁcations that apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. Typical AC electrical performance measured in demo board DC1464A (Figure 3, Test Circuit A) unless otherwise noted. Default operating conditions are VCC = 3.3V, EN = 0.8V, SHDN = 2.2V, +VG tied to VREF (negative gain slope mode), and ZSOURCE = ZLOAD = 50Ω unless otherwise noted.
PAGE 8
LTC6412 TYPICAL PERFORMANCE CHARACTERISTICS Electrical Performance in Test Circuits A and B at TA = 25°C and VCC = 3.3V unless otherwise noted.
PAGE 9
LTC6412 TYPICAL PERFORMANCE CHARACTERISTICS Electrical Performance in Test Circuits A and B at TA = 25°C and VCC = 3.3V unless otherwise noted. Gain (Sdd21) Conformance Error vs Control Voltage Over Temperature 20 5 15 GAIN (dB) 10 5 –V : NEGATIVE G SLOPE MODE 0 +VG: POSITIVE SLOPE MODE –5 –10 –40°C 25°C 85°C –15 –20 0 0.2 GAIN CONFORMANCE ERROR (dB) FREQ = 140MHz 20 FREQ = 140MHz 4 3 2 –40°C 1 25°C 0 –1 85°C –2 –3 –4 GMAX –5 0.4 0.8 1.0 0.6 +VG OR –VG VOLTAGE (V) 1.2 0 0.2 GMIN 0.
PAGE 10
LTC6412 TYPICAL PERFORMANCE CHARACTERISTICS Electrical Performance in Test Circuits A and B at TA = 25°C and VCC = 3.3V unless otherwise noted. 2nd Harmonic vs Distortion vs Control Voltage Over Frequency –20 3rd Harmonic Distortion vs Control Voltage Over Frequency –20 POUT = 0dBm Noise Figure at GMAX vs Frequency Over Temperature 14 POUT = 0dBm 85°C 12 –40 –60 –80 0 0.2 FREQ = 280MHz FREQ = 140MHz FREQ = 70MHz 0.4 0.6 0.8 –VG VOLTAGE (V) FREQ = 280MHz –80 FREQ = 70MHz FREQ = 140MHz GMIN 1.
PAGE 11
LTC6412 TYPICAL PERFORMANCE CHARACTERISTICS Electrical Performance in Test Circuits A and B at TA = 25°C and VCC = 3.3V unless otherwise noted. 10dB Gain Control Step 70MHz Time Domain Response –VG (0.
PAGE 12
LTC6412 PIN FUNCTIONS GND (Pins 1, 8, 12, 15, 18, 20, 23): Ground. Pins are connected to each other internally. For best RF performance, all ground pins should be connected to the printed circuit board ground plane. +IN (Pin 2): Positive Signal Input Pin. Has an internally generated DC Bias. A 10nF DC blocking capacitor is recommended. –IN (Pin 3): Negative Signal Input Pin. Has an internally generated DC Bias. A 10nF DC blocking capacitor is recommended. VCM (Pins 4, 5): Input Common Mode Voltage Pins.
PAGE 13
LTC6412 BLOCK DIAGRAM 6 13 VCC 19 VCC 24 VCC 22 21 SHDN VCC EN 15 23 GND GND REFERENCE AND BIAS CONTROL 2 +IN +OUT ••• BUFFER/ OUTPUT AMPLIFIER ••• 3 4 5 –IN –OUT ••• VCM DECL1 ATTENUATOR CONTROL VCM +VG 9 REFERENCE AND BIAS CONTROL –VG GND VREF 10 11 1 17 DECL2 GND GND GND GND EXPOSED PAD 8 12 15 18 25 16 7 14 6412 BD DC TEST CIRCUIT VCC 2.2V 0.8V 0.1μF SHDN VCM VCC 0.1μF EN VSUPPLY ≈ VCC + 2.3V 100Ω +IN +OUT +OUT LTC6412 –IN 0.
PAGE 14
LTC6412 OPERATION The LTC6412 employs an interpolated, tapped attenuator circuit architecture to generate the variable-gain characteristic of the ampliﬁer. The tapped attenuator is fed to a buffer and output ampliﬁer to complete the differential signal path shown in the Block Diagram. This circuit architecture provides good RF input power handling capability along with a constant output noise and output IP3 characteristic that are desirable for most IF signal chain applications.
PAGE 15
LTC6412 APPLICATIONS INFORMATION Introduction Port Characteristics The LTC6412 is a high linearity, fully-differential analogcontrolled variable-gain ampliﬁer (VGA) optimized for application frequencies in the range of 1MHz to 500MHz. The VGA architecture provides a constant OIP3 and constant output noise level (NF + Gain) over the 31dB gain-control range and thus exhibits a uniform spurious-free dynamic range (SFDR) over gain.
PAGE 16
LTC6412 APPLICATIONS INFORMATION grounding and supply decoupling. Failure to provide low impedance supply and ground at high frequencies can cause oscillations and increased distortion. Enable/Shutdown Both the EN pin and SHDN pin are self-biased to VCC through their respective 100k pull-up resistors, so the default open-pin state is powered on with the output ampliﬁer signal path disabled. Pulling the EN pin low completes the signal path from the attenuator ladder through the output ampliﬁer.
PAGE 17
LTC6412 APPLICATIONS INFORMATION ﬁltered to avoid AM upconversion artifacts. While using the ±VG turrets, a 4.7μF capacitor from the VGAIN SMA input to ground provides an effective lowpass ﬁlter. electrical characteristics such as low loss, broad band response and good phase matching. Typical data curves quoted for Test Circuit A are measured at the plane of the SMA connectors and are NOT corrected for any losses introduced by the input and output baluns, estimated at approximately 0.5dB and 1.
PAGE 18
LTC6412 APPLICATIONS INFORMATION Figure 9b shows a further variation of the tuned differential output where the DC blocking capacitors are brought inside the tank resonator to participate in the bandpass ﬁlter and transform the VGA output impedance to a lower value. Here too, the CO capacitor can be split into two separate shunt capacitors to ground, so any common mode noise is ﬁltered as well. Figure 9c shows a ﬂux transformer used to achieve a 50Ω single-ended output.
PAGE 19
LTC6412 APPLICATIONS INFORMATION SHDN EN VCC VCC R1 1k R2 [1] R3 [1] R4 1k VCC VCC C3 0.1μF R5 1k C2 1000pF R7 [1] 5 +IN 0dB 4 1 C8 10nF 2 2 3 3 R9 0Ω 4 5 C11 10nF 6 VCC C14 0.1μF 22 21 CB1 4.7μF 19 T2 4:1 C13 1000pF –IN 16 –OUT LTC6412 VCM GND VCM DECL2 VCC VCC 8 9 10 R15 0Ω 11 4 1 C6 0.1μF C20 [1] C9 [1] 2 5 • +OUT –OUT C21 0.1μF 15 14 13 C12 1000pF VCC C16 1000pF DECL1 GND +VG VREF –VG GND 7 VCC C7 0.1μF 17 +OUT +IN 3 18 GND VCC 12 C15 0.
PAGE 20
LTC6412 APPLICATIONS INFORMATION DIFFERENTIAL MODE PORT 1 50Ω COMMON MODE PORT 1 +IN 12.5Ω –IN 1:1 IDEAL TRANSFORMER WITH CENTER TAP +OUT DIFFERENTIAL MODE PORT 2 COMMON MODE PORT 2 200Ω 50Ω DUT –OUT 6412 F05 1:1 IDEAL TRANSFORMER WITH CENTER TAP Figure 5.
PAGE 21
LTC6412 APPLICATIONS INFORMATION 10mil LINE WIDTH +OUT (a) C1 0.1μF L1 = L2 C1 = C2 L1 VCC LTC6412 CO ZOUT = 200Ω DIFFERENTIAL 0.1μF NOTE: DASHED LINE COMPONENTS ARE FOR BANDPASS FILTERING (SEE TEXT) 0.1μF –OUT L2 C2 C1 L1 = L2 C1 = C2 +OUT (b) L1 VCC AT RESONANCE, CO LTC6412 0.1μF –OUT L2 C2 2 1 CO 200Ω ZOUT = 1 + 1 + 1 C1 C2 CO DIFFERENTIAL T2 4:1 +OUT (c) VCC T2 = MABAES0061 ZOUT = 50Ω SINGLE ENDED LTC6412 –OUT 0.1μF VCC 0.1μF L1 LCHOKE +OUT (d) C1 0.
PAGE 22
LTC6412 PACKAGE DESCRIPTION UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 p0.05 4.50 p 0.05 2.45 p 0.05 3.10 p 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 p0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 p 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 p 0.05 PIN 1 NOTCH R = 0.20 TYP OR 0.35 s 45o CHAMFER 23 24 PIN 1 TOP MARK (NOTE 6) 0.40 p 0.10 1 2 2.45 p 0.10 (4-SIDES) (UF24) QFN 0105 0.200 REF 0.00 – 0.05 0.25 p 0.05 0.50 BSC NOTE: 1.
PAGE 23
LTC6412 REVISION HISTORY REV DATE DESCRIPTION A 4/10 Change TCGAIN Typical to –0.007dB/°C in DC Electrical Characteristics PAGE NUMBER 3 6412fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PAGE 24
LTC6412 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS Fixed Gain IF Ampliﬁers/ADC Drivers LT1993-2, LT1993-4, LT1993-10 800MHz Differential Ampliﬁer/ADC Drivers –72dBc IM3 at 70MHz 2VP-P Composite, AV = 2V/V, 4V/V, 10V/V LTC6400-8, LTC6400-14, 1.8GHz Low Noise, Low Distortion Differential LTC6400-20, LTC6400-26 ADC Drivers –71dBc IM3 at 240MHz 2VP-P Composite, IS = 90mA, AV = 8dB, 14dB, 20dB, 26dB LTC6401-8, LTC6401-14, 1.