Datasheet

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LTC6406

6406fc

FEATURES

APPLICATIONS

DESCRIPTION

3GHz, Low Noise,

Rail-to-Rail Input Differential

Ampliﬁ er/Driver

The LTC

6406 is a very low noise, low distortion, fully

differential input/output ampliﬁ er optimized for 3V, single

supply operation. The LTC6406 input common mode range

is rail-to-rail, while the output common mode voltage is

independently adjustable by applying a voltage on the

OCM

pin. This makes the LTC6406 ideal for level-shifting

signals with a wide common mode range for driving 12-bit

to 16-bit single supply, differential input ADCs.

A 3GHz gain-bandwidth product results in 70dB linearity for

50MHz input signals. The LTC6406 is unity-gain stable and

the closed-loop bandwidth extends from DC to 800MHz.

The output voltage swing extends from near ground to

2V, to be compatible with a wide range of ADC converter

input requirements. The LTC6406 draws only 18mA, and

has a hardware shutdown feature which reduces current

consumption to 300μA.

The LTC6406 is available in a compact 3mm × 3mm 16-pin

leadless QFN package as well as an 8-lead MSOP package,

and operates over a –40°C to 85°C temperature range.

ADC Driver: Single-Ended Input to Differential Output with

Common Mode Level Shifting

Low Noise: 1.6nV/√Hz RTI

Low Power: 18mA at 3V

Low Distortion (HD2/HD3):

–80dBc/–69dBc at 50MHz, 2V

P-P

–104dBc/–90dBc at 20MHz, 2V

P-P

Rail-to-Rail Differential Input

2.7V to 3.5V Supply Voltage Range

Fully Differential Input and Output

Adjustable Output Common Mode Voltage

800MHz –3dB Bandwidth with A

= 1

Gain-Bandwidth Product: 3GHz

Low Power Shutdown

Available in 8-Lead MSOP and Tiny 16-Lead

3mm × 3mm × 0.75mm QFN Packages

Differential Input ADC Driver

Single-Ended to Differential Conversion

Level-Shifting Ground-Referenced Signals

Level-Shifting V

-Referenced Signals

High Linearity Direct Conversion Receivers

Harmonic Distortion vs Frequency

TYPICAL APPLICATION

–

150Ω

1.8pF

LTC6406

OCM

1.25V

150Ω

6406 TA01

+INA

–INA

LTC22xx ADC

GND

1.8pF

FREQUENCY (MHz)

6406 TA01b

DISTORTION (dBc)

= 3V

OCM

= V

ICM

= 1.25V

LOAD

= 800Ω

OUTDIFF

= 2V

P-P

DIFFERENTIAL INPUTS

–30

–40

–50

–60

–70

–80

–90

–110

–100

2ND, R

= R

= 150Ω

2ND, R

= R

= 500Ω

3RD, R

= R

= 150Ω

3RD, R

= R

= 500Ω

1 10010

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
LTC6406 3GHz, Low Noise, Rail-to-Rail Input Differential Amplifier/Driver FEATURES n n n n n n n n n n n DESCRIPTION Low Noise: 1.6nV/√Hz RTI Low Power: 18mA at 3V Low Distortion (HD2/HD3): –80dBc/–69dBc at 50MHz, 2VP-P –104dBc/–90dBc at 20MHz, 2VP-P Rail-to-Rail Differential Input 2.7V to 3.
PAGE 2
LTC6406 ABSOLUTE MAXIMUM RATINGS (Note 1) Total Supply Voltage (V+ to V–) ................................3.5V Input Current +IN, –IN, VOCM, SHDN, VTIP (Note 2) ...............±10mA Output Short-Circuit Duration (Note 3) ............ Indeﬁnite Operating Temperature Range (Note 4) .... –40°C to 85°C Speciﬁed Temperature Range (Note 5) .... –40°C to 85°C Junction Temperature ........................................... 150°C Storage Temperature Range...................
PAGE 3
LTC6406 DC ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V+ = 3V, V– = 0V, VCM = VOCM = VICM = 1.25V, VSHDN = open, RBAL = 100kΩ, RI = 150Ω, RF = 150Ω (0.1% resistors), CF = 1.8pF (see Figure 1) unless otherwise noted. VS is deﬁned as (V+ – V–). VOUTCM is deﬁned as (V+OUT + V–OUT)/2. VICM is deﬁned as (V+IN + V–IN)/2. VOUTDIFF is deﬁned as (V+OUT – V–OUT).
PAGE 4
LTC6406 DC ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V+ = 3V, V– = 0V, VCM = VOCM = VICM = 1.25V, VSHDN = open, RBAL = 100kΩ, RI = 150Ω, RF = 150Ω (0.1% resistors), CF = 1.8pF (see Figure 1) unless otherwise noted. VS is deﬁned as (V+ – V–). VOUTCM is deﬁned as (V+OUT + V–OUT)/2. VICM is deﬁned as (V+IN + V–IN)/2. VOUTDIFF is deﬁned as (V+OUT – V–OUT).
PAGE 5
LTC6406 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Input pins (+IN, –IN, VOCM, SHDN and VTIP) are protected by steering diodes to either supply. If the inputs should exceed either supply voltage, the input current should be limited to less than 10mA.
PAGE 6
LTC6406 TYPICAL PERFORMANCE CHARACTERISTICS 20 10 5 15 10 5 VSHDN = OPEN 0 0 0.5 1.0 1.5 2.0 2.5 SUPPLY VOLTAGE (V) 3.0 0 3.5 0.5 1.0 1.5 2.0 SHDN VOLTAGE (V) 2.5 en 1k 10k 100k FREQUENCY (Hz) INPUT VOLTAGE NOISE DENSITY (nV/√Hz) in 1 100 150 100 50 VSHDN = V– 0.5 1.0 1.5 2.0 2.5 SUPPLY VOLTAGE (V) 3.0 Differential Slew Rate vs Temperature 3 in 2 2 en 1 1 VS = 3V NOISE MEASURED AT f = 1MHz 0 0.5 1.0 1.5 2.0 2.5 INPUT COMMON MODE VOLTAGE (V) 0 3.
PAGE 7
LTC6406 TYPICAL PERFORMANCE CHARACTERISTICS Small-Signal Step Response (QFN Package) Large-Signal Step Response Output Overdrive Response 2.5 –OUT +OUT VOLTAGE (V) 2.0 0.2V/DIV 20mV/DIV +OUT 6406 G13 10ns/DIV VS = 3V VOCM = VICM = 1.25V RLOAD = 400Ω RI = RF = 150Ω, CF = 1.
PAGE 8
LTC6406 TYPICAL PERFORMANCE CHARACTERISTICS Harmonic Distortion vs Input Common Mode Voltage –40 –60 –50 DISTORTION (dBc) DISTORTION (dBc) –30 2ND, RI = RF = 150Ω 2ND, RI = RF = 500Ω 3RD, RI = RF = 150Ω 3RD, RI = RF = 500Ω –70 –80 –90 –110 1 10 FREQUENCY (MHz) –40 2ND, RI = RF = 150Ω 2ND, RI = RF = 500Ω 3RD, RI = RF = 150Ω 3RD, RI = RF = 500Ω –60 –70 –80 VS = 3V –90 VOCM = 1.25V VOUTDIFF = 2VP-P fIN = 50MHz RLOAD = 800Ω DIFFERENTIAL INPUTS –100 0 0.5 1.0 1.5 2.0 2.
PAGE 9
LTC6406 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response vs Load Capacitance 50 30 40 20 30 10 0 AV = 1 AV = 2 AV = 5 AV = 10 AV = 20 AV = 100 –20 –30 VS = 3V –40 VOCM = VICM = 1.25V RLOAD = 400Ω –50 1 10 100 FREQUENCY (MHz) 1000 2000 10 CL = 0pF CL = 2pF CL = 3pF CL= 4.7pF CL = 10pF 0 10 GAIN (dB) GAIN (dB) 20 Frequency Response vs Input Common Mode Voltage 5 0 –10 –20 VS = 3V –30 VOCM = VICM = 1.25V RLOAD = 400Ω –40 RI = RF = 150Ω, CF = 2.
PAGE 10
LTC6406 TYPICAL PERFORMANCE CHARACTERISTICS –40 VS = 3V –40 VOCM = VICM = 1.25V RLOAD = 800Ω = 2VP-P V –50 OUTDIFF SINGLE-ENDED INPUT –70 –80 2ND, RI = RF = 150Ω 2ND, RI = RF = 500Ω 3RD, RI = RF = 150Ω 3RD, RI = RF = 500Ω 10 10 FREQUENCY (MHz) 100 –60 2ND –70 VS = 3V VOCM = 1.25V fIN = 50MHz RLOAD = 800Ω RI = RF = 500Ω VOUTDIFF = 2VP-P SINGLE-ENDED INPUT –80 –90 3RD VS = 3V VOCM = VICM =1.25V –50 fIN = 50MHz RLOAD = 800Ω RI = RF = 500Ω SINGLE-ENDED INPUT –60 –70 2ND 3RD –80 –90 –100 –100 0 0.
PAGE 11
LTC6406 PIN FUNCTIONS (QFN/MSOP) is designed to drive a load capacitance of 5pF. Larger capacitive loads should be decoupled with at least 15Ω resistors from each output. mance, it is highly recommended that stray capacitance be kept to an absolute minimum by keeping printed circuit connections as short as possible. +OUTF, –OUTF (Pins 8, 13/NA): Filtered Output Pins. These pins have a series RC network (R = 50Ω, C = 3.75pF) connected between the ﬁltered and unﬁltered outputs.
PAGE 12
LTC6406 APPLICATIONS INFORMATION Functional Description The LTC6406 is a small outline, wideband, low noise, and low distortion fully-differential ampliﬁer with accurate output phase balancing. The LTC6406 is optimized to drive low voltage, single-supply, differential input analogto-digital converters (ADCs). The LTC6406 input common mode range is rail-to-rail, while the output common mode voltage is independently adjustable by applying a voltage on the VOCM pin.
PAGE 13
LTC6406 APPLICATIONS INFORMATION CF 0.1μF RI RF V+IN 100Ω V–OUT RT 16 15 NC 14 +IN –OUT V–OUTF 13 SHDN • V– 12 1 – 0.1μF V– V 2 + + 1.25pF V+ VOCM V– – V– 3 V 50Ω 100k V+ 50Ω 1.25pF VOCM VVOCM 4 5 VTIP 6 –IN 7 +OUT 0.01μF RT 0.1μF RI V–IN 8 MINI-CIRCUITS TCM4-19 0.1μF – V– V+ 11 0.1μF V– V– 0.1μF V– +OUTF 50Ω V+ V+ 10 9 0.01μF V– • VSHDN V+ RT CHOSEN SO THAT RT||RI = 100Ω LTC6406 1.25pF SHDN + VIN –OUTF • • 50Ω MINI-CIRCUITS TCM4-19 0.
PAGE 14
LTC6406 APPLICATIONS INFORMATION Δβ is deﬁned as the difference in feedback factors: General Ampliﬁer Applications As levels of integration have increased and correspondingly, system supply voltages decreased, there has been a need for ADCs to process signals differentially in order to maintain good signal to noise ratios. These ADCs are typically supplied from a single supply voltage which can be as low as 3V, and will have an optimal common mode input range of 1.25V or 1.5V.
PAGE 15
LTC6406 APPLICATIONS INFORMATION In general, the degree of feedback pair mismatch is a source of common mode to differential conversion of both signals and noise. Using 1% resistors or better will mitigate most problems, and will provide about 34dB worst case of common mode rejection. Using 0.1% resistors will provide about 54dB of common mode rejection. A low impedance ground plane should be used as a reference for both the input signal source and the VOCM pin. Bypassing the VOCM with a high quality 0.
PAGE 16
LTC6406 APPLICATIONS INFORMATION Input Common Mode Voltage Range Manipulating the Rail-to-Rail Input Stage with VTIP The LTC6406’s input common mode voltage (VICM) is deﬁned as the average of the two input voltages, V+IN, and V–IN. At the inputs to the actual op amp, the range extends from V– to V+. This makes it easy to interface to a wide range of common mode signals, from ground referenced to VCC referenced signals.
PAGE 17
LTC6406 APPLICATIONS INFORMATION Output Common Mode Voltage Range The output common mode voltage is deﬁned as the average of the two outputs: VOUTCM = VOCM = V+OUT + V–OUT 2 The VOCM pin sets this average by an internal common mode feedback loop which internally forces VOUTCM = VOCM. The output common mode range extends from 0.5V above V– to 1V below V+. The VOCM voltage is internally set by a resistive divider between the supplies, developing a default voltage potential of 1.25V with a 3V supply.
PAGE 18
LTC6406 APPLICATIONS INFORMATION the ﬁltered outputs, which also halves the ﬁlter bandwidth. Combinations of capacitors could be used as well; a three capacitor solution of 1.2pF from each ﬁltered output to ground plus a 1.2pF capacitor between the ﬁltered outputs would also halve the ﬁlter bandwidth (Figure 8). driven differentially it will appear at each ﬁltered output as a single-ended capacitance of twice the value. To halve the ﬁlter bandwidth, for example, two 3.
PAGE 19
LTC6406 APPLICATIONS INFORMATION Noise Considerations 100 2 eno = ⎛ ⎛ RF ⎞ ⎞ 2 ⎜ eni • ⎜ 1+ R ⎟ ⎟ + 2 • (In • RF ) + ⎝ ⎝ I ⎠⎠ A plot of this equation, and a plot of the noise generated by the feedback components for the LTC6406 is shown in Figure 10. RI RF FEEDBACK NETWORK NOISE ALONE 1 0.1 10 1k 10k RI = RF (Ω) 6406 F10 The LTC6406’s input referred voltage noise contributes the equivalent noise of a 155Ω resistor.
PAGE 20
LTC6406 APPLICATIONS INFORMATION Layout Considerations Because the LTC6406 is a very high speed ampliﬁer, it is sensitive to both stray capacitance and stray inductance. In the QFN package, three pairs of power supply pins are provided to keep the power supply inductance as low as possible to prevent any degradation of ampliﬁer 2nd harmonic performance. It is critical that close attention be paid to supply bypassing. For single supply applications it is recommended that high quality 0.
PAGE 21
LTC6406 APPLICATIONS INFORMATION from properly dampening the load transient caused by the sampling process, prolonging the time required for settling. In 16-bit applications, this will typically require a minimum of 11 R-C time constants. It is recommended that the capacitor chosen have a high quality dielectric (such as C0G multilayer ceramic). 1.8pF VIN, 2VP-P 150Ω 150Ω 16 15 NC +IN 14 –OUT 13 SHDN –OUTF LTC6406 1.25pF SHDN V– 12 1 V+ 0.1μF 50Ω 100k V+ 2 3.3V 1.
PAGE 22
LTC6406 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ±0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 PIN 1 TOP MARK (NOTE 6) 16 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1.
PAGE 23
LTC6406 PACKAGE DESCRIPTION MS8E Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1662) BOTTOM VIEW OF EXPOSED PAD OPTION 2.06 ± 0.102 (.081 ± .004) 1 5.23 (.206) MIN 1.83 ± 0.102 (.072 ± .004) 0.889 ± 0.127 (.035 ± .005) 2.794 ± 0.102 (.110 ± .004) 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 8 0.42 ± 0.038 (.0165 ± .0015) TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.65 (.0256) BSC 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ± 0.102 (.118 ± .
PAGE 24
LTC6406 TYPICAL APPLICATIONS Attenuating and Level Shifting a Single-Ended ±5V Signal to a Differential 2VP-P Signal at a 1.25V Common Mode C1, 2.7pF 2VP-P DIFF OUTPUT LEVEL-SHIFTED TO 1.25V R3, 100Ω 3.3V 3.3V R5 511Ω p5V SINE WAVE (10VP-P) CENTERED AT 0V VIN R1 51.1Ω – + R6 511Ω R2 51.1Ω LTC6406 + – LTC2207 6406 TA03 VCM = 1.25V R4, 100Ω C2, 2.7pF Second Order 30MHz 0.5dB Chebyshev Differential Input/Output Lowpass Filter R1, 150Ω 3.3V C1, 8.