Datasheet

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LT6411

6411f

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

650MHz Differential ADC

Driver/Dual Selectable

Gain Ampliﬁ er

The LT

6411 is a dual ampliﬁ er with individually selectable

gains of +1, +2 and –1. The ampliﬁ ers have excellent dis-

tortion performance for driving ADCs as well as excellent

bandwidth and slew rate for video, data transmission and

other high speed applications. Single-ended to differential

conversion with a system gain of 2 is particularly straight-

forward by conﬁ guring one ampliﬁ er with a gain of +1

and the other ampliﬁ er with a gain of –1. The LT6411 can

be used on split supplies as large as ±6V and on a single

supply as low as 4.5V.

Each ampliﬁ er draws only 8mA of quiescent current when

enabled. When disabled, the output pins become high

impedance and each ampliﬁ er draws less than 350µA.

The LT6411 is manufactured on Linear Technology’s

proprietary, low voltage, complimentary, bipolar process

and is available in the ultra-compact, 3mm × 3mm, 16pin

QFN package.

■

650MHz –3dB Small-Signal Bandwidth

■

600MHz –3dB Large-Signal Bandwidth

■

High Slew Rate: 3300V/µs

■

Easily Conﬁ gured for Single-Ended to Differential

Conversion

■

200MHz ±0.1dB Bandwidth

■

User Selectable Gain of +1, +2 and –1

■

No External Resistors Required

■

46.5dBm Equivalent OIP3 at 30MHz When Driving an

ADC

■

IM3 with 2V

P-P

Composite, Differential Output:

–87dBc at 30MHz, –83dBc at 70MHz

■

–77dB SFDR at 30MHz, 2V

P-P

Differential Output

■

6ns 0.1% Settling Time for 2V Step

■

Low Supply Current: 8mA per Ampiﬁ er

■

Differential Gain of 0.02%, Differential Phase of 0.01°

■

50dB Channel Separation at 100MHz

■

Wide Supply Range: ±2.25V (4.5V) to ±6.3V (12.6V)

■

3mm × 3mm 16-Pin QFN Package

■

Differential ADC Driver

■

Single-Ended to Differential Conversion

■

Differential Video Line Driver

Differential ADC Driver

30MHz 2-Tone 32768 Point FFT, LT6411

Driving an LTC

2249 14-Bit ADC

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

–

6411 TA01a

LTC2249

14-BIT ADC

80Msps

–

DGND

LT6411

30MHz

1.9V

INPUT

370Ω 370Ω

24Ω

370Ω 370Ω

FREQUENCY (MHz)

–140

AMPLITUDE (dBFS)

–120

–100

–80

–40

20 40

6411 TA01b

–20

–60

–130

–110

–90

–10

–50

–30

–70

30 35

32768 POINT FFT

TONE 1 AT 29.5MHz, –7dBFS

TONE 2 AT 30.5MHz, –7dBFS

IM3 = –87dBc

Summary of content (16 pages)

PAGE 1
LT6411 650MHz Differential ADC Driver/Dual Selectable Gain Amplifier DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 650MHz –3dB Small-Signal Bandwidth 600MHz –3dB Large-Signal Bandwidth High Slew Rate: 3300V/µs Easily Conﬁgured for Single-Ended to Differential Conversion 200MHz ±0.1dB Bandwidth User Selectable Gain of +1, +2 and –1 No External Resistors Required 46.
PAGE 2
LT6411 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) Total Supply Voltage (VCC to VEE) ..........................12.6V Input Current (Note 2)..........................................±10mA Output Current (Continuous) ...............................±70mA EN to DGND Voltage (Note 2) ..................................5.5V Output Short-Circuit Duration (Note 3) ............ Indeﬁnite Operating Temperature Range (Note 4) ... –40°C to 85°C Speciﬁed Temperature Range (Note 5) ....
PAGE 3
LT6411 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VS = ±5V, AV = 2, RL = 150Ω, CL = 1.5pF, VEN = 0.4V, VDGND = 0V, unless otherwise noted.
PAGE 4
LT6411 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VCC = 5V, VEE = 0V, AV = 2, No RLOAD, VEN = 0.4V, VDGND = 0V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 30MHz Signal HD Second/Third Harmonic Distortion 2VP-P Differential 2VP-P Differential, RL = 200Ω Differential –77 –64 dBc dBc IMD330M Third-Order IMD 2VP-P Differential Composite, f1 = 29.
PAGE 5
LT6411 TYPICAL PERFORMANCE CHARACTERISTICS All measurements are per ampliﬁer with single-ended outputs unless otherwise noted. Supply Current per Ampiﬁer vs Supply Voltage Supply Current per Ampliﬁer vs Temperature VEN = 0V 8 VEN = 0.4V 6 VCC = –VEE VEN, VDGND, VIN+, VIN– = 0V 10 TA = 25°C SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 10 4 12 12 VS = ±5V RL = ∞ VIN+, VIN– = 0V 2 8 6 4 0 1 2 20 5 0 –5 –10 VS = ±5V AV = 2 3.5 0 TA = 125°C –20 4.
PAGE 6
LT6411 TYPICAL PERFORMANCE CHARACTERISTICS All measurements are per ampliﬁer with single-ended outputs unless otherwise noted. Positive Input Impedance vs Frequency Input Noise Spectral Density 1000 VS = ±5V AV = 2 TA = 25°C en in 10 70 VS = ±5V VIN = 0V TA = 25°C 10 1 VS = ±5V AV = 2 TA = 25°C ±PSRR 60 REJECTION RATIO (dB) 100 PSRR vs Frequency 100 INPUT IMPEDANCE (kΩ) INPUT NOISE (nV/√Hz OR pA/√Hz) 1000 50 –PSRR 40 +PSRR 30 20 10 1 0.01 0.1 1 FREQUENCY (kHz) 10 0.1 0.01 100 0.
PAGE 7
LT6411 TYPICAL PERFORMANCE CHARACTERISTICS All measurements are per ampliﬁer with single-ended outputs unless otherwise noted. Third Order Intermodulation Distortion vs Frequency, Differential Input Output Third Order Intercept vs Frequency, Differential Input 0 –30 –40 RL = 200Ω –70 RL = 200Ω 30 VOUT = 2VP-P, COMPOSITE, DIFFERENTIAL 1MHz TONE SPACING AV = 2, VCC = 5V VEE = 0V, VCM = 1.
PAGE 8
LT6411 PIN FUNCTIONS VEE (Pins 1, 2): Negative Supply Voltage. VEE pins are not internally connected to each other and must all be connected externally. Proper supply bypassing is necessary for best performance. See the Applications Information section. VEE (Pins 3, 7): Negative Supply Voltage for Output Stage. VEE pins are not internally connected to each other and must all be connected externally. Proper supply bypassing is necessary for best performance. See the Applications Information section.
PAGE 9
LT6411 APPLICATIONS INFORMATION Since the EN pin is referenced to DGND, it may need to be pulled below ground in those cases. In order to protect the internal enable circuitry, the EN pin should not be forced more than 0.5V below DGND. Power Supplies The LT6411 can be operated on as little as ±2.25V or a single 4.5V supply and as much as ±6V or a single 12V supply. Internally, each supply is independent to improve channel isolation.
PAGE 10
LT6411 APPLICATIONS INFORMATION Input Considerations The LT6411 input voltage range is from VEE + 1V to VCC – 1V. Therefore, on split supplies the LT6411 input range is always as large as or larger than the output swing. On a single positive supply with a gain of +2 and IN– connected to ground, however, the input range limit of +1V limits the linear output low swing to 2V (1V multiplied by the internal gain of 2).
PAGE 11
LT6411 APPLICATIONS INFORMATION +V the output signals can be AC coupled and DC biased in a manner similar to what is shown at the inputs in Figure 3. A simpler alternative when using an ADC such as the LTC2249 is to use the ADC’s VCM pin to set the optimal common mode voltage as shown in Figure 5. If unity common mode gain and difference mode response to DC is desired, there is another conﬁguration available.
PAGE 12
LT6411 APPLICATIONS INFORMATION Layout and Grounding It is imperative that care is taken in PCB layout in order to utilize the very high speed and very low crosstalk of the LT6411. Separate power and ground planes are highly recommended and trace lengths should be kept as short as possible. If input or output traces must be run over a distance of several centimeters, they should use a controlled impedance with matching series and shunt resistances to maintain signal ﬁdelity.
PAGE 13
LT6411 AMPLITUDE (dBFS) TYPICAL APPLICATIONS 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 –120 –130 –140 5V 32768 POINT FFT TONE 1 AT 29.5MHz, –7dBFS TONE 2 AT 30.5MHz, –7dBFS IM3 = –90dBc IN+ 13 14 15 IN– 16 + 6,9,10 LT6411 AV = 2 – 50Ω 50Ω 100Ω 5 1,2,3,7 RECEIVER 6411 F10 11,12 –5V Figure 10. Twisted-Pair Driver 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40 6411 F09 Figure 9. 2-Tone Response of the LT6411 Conﬁgured with Single-Ended Inputs Driving the LTC2249 at 29.5MHz, 30.
PAGE 14
LT6411 TYPICAL APPLICATIONS VCC CD1 0.1µF + VEE C1 OPT “B” CASE CD2 4700pF VCC VCC 3 R7 R37 OPT 2 4 R3 6 R5 C5 C9 R38 OPT C8 TBD 0603 R13 L2 TBD 0603 CD4 0.1µF C3 R6 T1 TBD ETC1-1TTR 0603 5 1 J2 AIN– R2 OPT C2 R10 C11 13 IN1– 15 IN2– 16 IN2+ OUT1 8 R8 10Ω 1% 5 R11 10Ω 1% 1 R9 10Ω 1% LT6411 VEE OUT2 2 3 7 C6 L1 TBD R12 0603 10Ω 1% R35 12.1Ω 1% C4 R36 12.
PAGE 15
LT6411 SIMPLIFIED SCHEMATIC VCC VCC TO OTHER AMPLIFIER BIAS IN– 370Ω VCC 46k 1k IN+ EN 150Ω 370Ω OUT VEE DGND VEE 6411 SS VEE PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) BOTTOM VIEW—EXPOSED PAD 3.00 ± 0.10 (4 SIDES) 0.70 ±0.05 15 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 16 1 1.45 ± 0.10 (4-SIDES) 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.
PAGE 16
LT6411 TYPICAL APPLICATION 80.6Ω 5V IN+ + – – + 1.9VDC IN– 1.9VDC 55Ω 390nH 10Ω 55Ω 80.6Ω 9 6 3 0 –3 –6 AIN– 15pF 390nH LT6411 or additional ﬁltering. Figure 15 shows the corresponding SFDR of –75.5dBc with a 30MHz tone. Figure 16 shows the 2-tone response of the LT6411 with 29.5MHz and 30.5MHz inputs. Note that 0dBFS corresponds to a 2VP-P differential signal.