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LTC6409

6409fa

LTC6409 Driving LTC2262-14 ADC,

= 70MHz, –1dBFS,

= 150MHz, 4096-Point FFT

Typical applicaTion

DescripTion

10GHz GBW, 1.1nV/√Hz

Differential Amplifier/ADC

Driver

The LTC

6409 is a very high speed, low distortion, dif-

ferential amplifier. Its input common mode range includes

ground, so that a ground-referenced input signal can be

DC-coupled, level-shifted, and converted to drive an ADC

differentially.

The gain and feedback resistors are external, so that the

exact gain and frequency response can be tailored to each

application. For example, the amplifier could be externally

compensated in a no-overshoot configuration, which is

desired in certain time-domain applications.

The LTC6409 is stable in a differential gain of 1. This al-

lows for a low output noise in applications where gain is

not desired. It draws 52mA of supply current and has a

hardware shutdown feature which reduces current con-

sumption to 100µA.

The LTC6409 is available in a compact 3mm × 2mm 10-pin

leadless QFN package and operates over a –40°C to 125°C

temperature range.

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.

DC-Coupled Interface from a Ground-Referenced Single-Ended

Input to an LTC2262-14 ADC

FeaTures

applicaTions

10GHz Gain-Bandwidth Product

88dB SFDR at 100MHz, 2V

P-P

1.1nV/√Hz Input Noise Density

Input Range Includes Ground

External Resistors Set Gain (Min 1V/V)

3300V/µs Differential Slew Rate

52mA Supply Current

2.7V to 5.25V Supply Voltage Range

Fully Differential Input and Output

Adjustable Output Common Mode Voltage

Low Power Shutdown

Small 10-Lead 3mm × 2mm × 0.75mm QFN Package

Differential Pipeline ADC Driver

High-Speed Data-Acquisition Cards

Automated Test Equipment

Time Domain Reflexometry

Communications Receivers

–

150Ω

1.3pF

LTC6409

OCM

= 0.9V

33.2Ω

10Ω

150Ω

6409 TA01

–

LTC2262-14 ADC

GND

1.8V

3.3V

1.3pF

39pF

FREQUENCY (MHz)

6409 TA01b

AMPLITUDE (dBFS)

–80

–70

–60

–50

–40

–30

–20

–10

–90

–100

–110

–120

0 704010 5020 6030

= 3.3V

OUTDIFF

= 1.8V

P-P

HD2 = –86.5dBc

HD3 = –89.4dBc

SFDR = 81.6dB

SNR = 71.1dB

Summary of content (24 pages)

PAGE 1
LTC6409 10GHz GBW, 1.1nV/√Hz Differential Amplifier/ADC Driver Description Features n n n n n n n n n n n n 10GHz Gain-Bandwidth Product 88dB SFDR at 100MHz, 2VP-P 1.1nV/√Hz Input Noise Density Input Range Includes Ground External Resistors Set Gain (Min 1V/V) 3300V/µs Differential Slew Rate 52mA Supply Current 2.7V to 5.25V Supply Voltage Range Fully Differential Input and Output Adjustable Output Common Mode Voltage Low Power Shutdown Small 10-Lead 3mm × 2mm × 0.
PAGE 2
LTC6409 Absolute Maximum Ratings Pin Configuration (Note 1) 2 V+ V– 9 8 11,V– 3 4 5 VOCM +IN 10 V+ 1 SHDN –OUT V– TOP VIEW Total Supply Voltage (V+ – V–)..................................5.5V Input Current (+IN, –IN, VOCM, SHDN) (Note 2)................................................................. ±10mA Output Short-Circuit Duration (Note 3)............. Indefinite Operating Temperature Range (Note 4)...................................................
PAGE 3
LTC6409 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = 0V, VCM = VOCM = VICM = 1.25V, VSHDN = open. 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
LTC6409 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = 0V, VCM = VOCM = VICM = 1.25V, VSHDN = open. 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
LTC6409 Electrical Characteristics Note 7: Input common mode range is tested by testing at both VICM = 1.25V and at the Electrical Characteristics table limits to verify that the differential offset (VOSDIFF) and the common mode offset (VOSCM) have not deviated by more than ±1mV and ±2mV respectively from the VICM = 1.25V case. The voltage range for the output common mode range is tested by applying a voltage on the VOCM pin and testing at both VOCM = 1.
PAGE 6
LTC6409 Typical Performance Characteristics Differential Output Voltage Noise vs Frequency 10 1 1 1k 1M FREQUENCY (Hz) 100 100 in 10 10 en 1 1G 1 1 1G 1k 1M FREQUENCY (Hz) 6409 G07 CMRR vs Frequency 1000 1000 VS = 5V OUTPUT IMPEDANCE (Ω) 100 1000 INPUT VOLTAGE NOISE DENSITY (nV/√Hz) VS = 5V RI = RF = 150Ω INCLUDES RI/RF NOISE INPUT CURRENT NOISE DENSITY (pA/√Hz) VOLTAGE NOISE DENSITY (nV/√Hz) 1000 Differential Output Impedance vs Frequency Input Noise Density vs Frequency VS = 5V
PAGE 7
LTC6409 Typical Performance Characteristics Frequency Response vs Closed Loop Gain 50 40 GAIN (dB) 30 20 10 0 20 AV = 400 AV = 100 AV (V/V) RI (Ω) 1 2 5 10 20 100 400 AV = 20 AV = 10 AV = 5 AV = 2 AV = 1 –10 VS = 5V –20 VOCM = VICM = 1.25V RLOAD = 400Ω –30 1 10 100 1000 FREQUENCY (MHz) 150 100 50 50 25 25 25 10000 6409 G15 Gain 0.1dB Flatness 3400 0.4 3375 0.3 SLEW RATE (V/µs) 0 –0.1 VS = 5V VOCM = VICM = 1.25V –0.4 RLOAD = 400Ω RI = RF = 150Ω, CF = 1.3pF –0.
PAGE 8
LTC6409 Typical Performance Characteristics Harmonic Distortion vs Output VS = 5V VICM = 1.25V VOCM =Voltage Common Mode –40 –50 DISTORTION (dBc) –80 –90 HD2 –100 –60 –70 –80 1 10 100 FREQUENCY (MHz) –120 –2 –4 (0.4VP-P) 1 1.5 2 2.5 3 3.
PAGE 9
LTC6409 Block Diagram 2 1 +IN –OUT V– 3 SHDN V+ V+ + 200k V+ 5 VOCM – 50k V– 4 V+ 10 V– 9 V+ V– V+ V– 6 –IN 7 8 V– +OUT 6409 BD Applications Information Functional Description The LTC6409 is a small outline, wideband, high speed, low noise, and low distortion fully-differential amplifier with accurate output phase balancing. The amplifier is optimized to drive low voltage, single-supply, differential input analogto-digital converters (ADCs).
PAGE 10
LTC6409 Applications Information RI V+IN RF V–OUT + VINP – + VCM – + VVOCM VOCM – VICM = – VINM + RI V–IN RF 6409 F01 V+OUT Figure 1. Circuit for Common Mode Range suited for pre-amplification, level shifting and conversion of single-ended signals to differential output signals for driving differential input ADCs. Output Common Mode and VOCM Pin The output common mode voltage is defined as the average of the two outputs: VOUTCM = VOCM = that can be processed is even wider.
PAGE 11
LTC6409 Applications Information a termination resistor RT should be chosen (see Figure 2) such that: RI2 VINP VOCM – VINM + RI1 V–IN RF1 6409 F03 V+OUT Figure 3.
PAGE 12
LTC6409 Applications Information resistor mismatch can make the apparent voltage offset of the amplifier appear worse than specified. enRI2 RI RF in+2 The apparent input referred offset induced by feedback factor mismatch is derived from Equation (3): VOSDIFF(APPARENT) ≈ (VCM – VOCM) • Δβ + Using the LTC6409 in a single 5V supply application with 0.1% resistors, the input common mode grounded, and the VOCM pin biased at 1.25V, the worst case mismatch can induce 1.25mV of apparent offset voltage.
PAGE 13
LTC6409 Applications Information enRI2 RI Finally, noise figure can be obtained as: enRF2 RF  eno2 NF = 10log  1+  eno2(RS) in+2 RS RT + eno2 VOCM enRS2 in–2 enRT2 enRI2 – eni2 RI enRF2 RF 6409 F06 Figure 6. A More General Noise Model Including Source and Termination Resistors calculation, a termination resistor (RT) is included and its noise contribution is taken into account.
PAGE 14
LTC6409 Applications Information 1.3pF 150Ω 1:4 50Ω VIN + – 150Ω + 600Ω VOCM – 150Ω 1:4 VIN VIN 100Ω eno = 5.77nV/√Hz NF = 10.43dB VIN VOCM + – – 100Ω 1pF 0.4pF 0.8pF VOCM – 50Ω eno = 11.69nV/√Hz NF = 8.81dB 500Ω VIN VOCM + – – 50Ω 0.4pF NF = 16.66dB 250Ω + 50Ω eno = 9.76nV/√Hz 200Ω 1pF 500Ω NF = 17.59dB 200Ω + 50Ω eno = 5.88nV/√Hz 150Ω 1pF + 100Ω – 150Ω 200Ω 100Ω VOCM + – 1pF – + – VIN 1.3pF VOCM 1:4 NF = 14.41dB + 50Ω 200Ω 100Ω 50Ω eno = 4.
PAGE 15
LTC6409 Applications Information results in a lower intercept point. Therefore, it is important to consider the impedance seen by the output of the LTC6409 when working with intercept points. ∆f = f2 – f1 = f1 – (2f1 – f2) = (2f2 – f1) – f2 PO POWER PO Comparing linearity specifications between different amplifier types becomes easier when a common impedance level is assumed. For this reason, the intercept points for LTC6409 are reported normalized to a 50Ω load impedance.
PAGE 16
LTC6409 Applications Information between the RL • 4 = 200Ω differential resistance seen at location B and the 200Ω formed by the two 100Ω matching resistors at the LTC6409 output. Thus, the differential power at location B is 10 – 6 = 4dBm. Since the transformer ratio is 4:1 and it has an insertion loss of about 1dB, the power at location C (across RL) is calculated to be 4 – 6 – 1 = –3dBm.
PAGE 17
LTC6409 Applications Information Board Layout and Bypass Capacitors Driving ADCs For single supply applications, it is recommended that high quality 0.1µF||1000pF ceramic bypass capacitors be placed directly between each V+ pin and its closest V– pin with short connections. The V– pins (including the Exposed Pad) should be tied directly to a low impedance ground plane with minimal routing.
PAGE 18
LTC6409 Applications Information 1.3pF VIN 150Ω 150Ω 2 +IN 33.2Ω 1 –OUT LTC6409 SHDN SHDN V– 3 V+ 5V 4 V+ V+ VOCM V+ 9 5V – 5 V VOCM V– 0.1µF 6 150Ω –IN 150Ω 10Ω 0.1µF||1000pF + 0.1µF||1000pF CONTROL V– 10 7 0.1µF||1000pF – AIN+ 39pF 10Ω 39pF LTC2262-14 ADC AIN– VCM GND VDD D13 • • D0 1.8V 1µF 8 +OUT 1µF 6409 F11 33.2Ω 100Ω 1.3pF Figure 11.
PAGE 19
LTC6409 Applications Information R5 150Ω, 0.1% C22 1.3pF V+ J1 IN T1 TCM4-19 1:4 XFMR MINI-CIRCUITS Sd 3 R14 0Ω 4 C23 0.1µF 6 Pd R13 OPT C25 0.1µF CT 2 4 P S 1 R9 150Ω, 0.1% C24 0.1µF 2 5 R10 150Ω, 0.1% R12 300Ω 6 3 R11 300Ω V+ 1 –OUT C19 0.1µF LTC6409UDB VOCM –IN SHDN R3 100Ω V– V– +OUT 7 V– 11 10 T2 TCM4-19 4:1 XFMR MINI-CIRCUITS 1 S C18 0.1µF C29 0.1µF P R1 0Ω 4 2 CT 3 R2 OPT Pd 6 Sd J2 OUT R4 100Ω 8 VCM C32 0.
PAGE 20
LTC6409 Applications Information Figure 13.
PAGE 21
LTC6409 Typical Applications DC-Coupled Level Shifting of an I/Q Demodulator Output C5 0.9pF 5V LT5575 5V 5V 65Ω 65Ω I RF IN 1900MHz –10dBm 200mVP-P 5V LO 1920MHz 0dBm 5V C1 10pF 5V R1 75Ω R3 75Ω R2 75Ω C3 R4 12pF 75Ω –OUT LTC6409 – + +OUT VOCM 1.25V 65Ω 65Ω 3.4dBm 936mVP-P + – C2 10pF 5pF 5pF Q –8.9dBm 227mVP-P DC LEVEL 1.25V R5 620Ω DC LEVEL 3.9V 5pF 5pF DC LEVEL 3.4V DIFF OUTPUT Z 130Ω| |2.5pF R6 620Ω IDENTICAL Q CHANNEL C4 0.9pF 6409 TA02 GAIN: 1.1dB GAIN: 12.
PAGE 22
LTC6409 Package Description UDB Package 10-Lead Plastic QFN (3mm × 2mm) (Reference LTC DWG # 05-08-1848 Rev A) 0.25 ± 0.05 0.95 ± 0.05 0.65 ±0.05 2.50 ±0.05 1.10 ±0.05 0.75 ±0.05 0.90 ± 0.05 0.05 ± 0.05 DETAIL B DETAIL B PACKAGE OUTLINE 0.25 ± 0.10 0.25 ± 0.05 0.50 BSC 0.85 ± 0.05 3.50 ±0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.40 ± 0.10 2.00 ± 0.05 3.00 ± 0.05 0.20 REF SIDE VIEW 0.90 ± 0.10 0.05 ± 0.10 DETAIL A R = 0.13 TYP 8 10 0.80 7 BSC 6 0.70 ± 0.10 1 DETAIL A 2 5 3 0.60 ± 0.
PAGE 23
LTC6409 Revision History REV DATE DESCRIPTION PAGE NUMBER A 12/10 Revised Typical Application drawing 21 6409fa 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
LTC6409 Typical Applications LTC6409 Externally Compensated for Maximum Gain Flatness and for No-Overshoot Time-Domain Response 1.3pF Gain 0.1dB Flatness 0.5 150Ω 0.1µF 75Ω PORT 1 50Ω 150Ω VOCM = 1.25V 0.1µF PORT 2 50Ω 0.4 5V 75Ω 150Ω – + LTC6409 + – 150Ω 150Ω 0.1µF 0.1µF 0.3 1/2 AGILENT E5071A PORT 3 50Ω 0.2 GAIN (dB) 1/2 AGILENT E5071A PORT 4 50Ω 0.1 0 –0.1 –0.2 –0.3 150Ω –0.4 –0.5 1.3pF 1.2pF 1 10 100 1000 FREQUENCY (MHz) 10000 No-Overshoot Step Response 250Ω 0.