Datasheet

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LTC6416

6416f

The LTC

6416 is a differential unity gain buffer designed

to drive 16-bit ADCs with extremely low output noise

and excellent linearity beyond 300MHz. Differential input

impedance is 12k, allowing 1:4 and 1:8 transformers to

be used at the input to achieve additional system gain.

With no external biasing or gain setting components and

a ﬂ ow-through pinout, the LTC6416 is very easy to use.

It can be DC-coupled and has a common mode output

offset of –40mV. If the input signals are AC-coupled, the

LTC6416 input pins are internally biased to provide an

output common mode voltage that is set by the voltage

on the V

pin.

In addition the LTC6416 has high speed, fast recovery

clamping circuitry to limit output signal swing. Both the

high and low clamp voltages are internally biased to allow

maximum output swing but are also user programmable

via the CLLO and CLHI pins.

Supply current is nominally 42mA and the LTC6416 oper-

ates on supply voltages ranging from 2.7V to 3.9V.

The LTC6416 is packaged in a 10-lead 3mm × 2mm DFN

package. Pinout is optimized for placement directly adjacent

to Linear’s high speed 12-, 14- and 16-bit ADCs.

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

trademarks are the property of their respective owners.

TYPICAL APPLICATION

DESCRIPTION

2 GHz Low Noise Differential

16-Bit ADC Buffer

LTC6416 Driving LTC2208 ADC – 140MHz IF

FEATURES

APPLICATIONS

2GHz –3dB Small Signal Bandwidth

300MHz ±0.1dB Bandwidth

1.8nV/√Hz Output Noise

46.25dBm Equivalent OIP3 at 140MHz

40.25dBm Equivalent OIP3 Up to 300MHz

–81dBc/–72dBc HD2/HD3 at 140MHz, 2V

P-P

Out

–84.5dBc IM3 at 140MHz, 2V

P-P

Out Composite

–74dBc/–67.5dBc HD2/HD3 at 300MHz, 2V

P-P

Out

–72.5dBc IM3 at 300MHz, 2V

P-P

Out Composite

Programmable High Speed, Fast Recovery

Output Clamping

DC-Coupled Signal Path

Operates on Single 2.7V to 3.9V Supply

Low Power: 150mW on 3.6V

2mm × 3mm 10-Pin DFN Package

Differential ADC Driver

IF Sampling Receivers

Impedance Transformer

SAW Filter Interface

CCD Buffer

25

200

1pF

GND

OUT

–

6416 TA01a

OUT

1.5pF

0.1µF

3.6V

2.2µF

25

3.3V

1:8

MINI-CIRCUITS

TCM8-1+

50

–

AIN

–

PGA = 1

LTC2208

CLHI

CLLO

–

LTC6416

680pF

CLOCK

(130MHz)

FREQUENCY (MHz)

AMPLITUDE (dBFS)

6416 TA01b

–120

–110

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

3020

40 50

= 3.6V

HD2 = –94dBc

HD3 = –89.1dBc

SFDR = 89.1dB

SNR = 70.7dB

MEASURED USING DC1257B

WITH MINI-CIRCUIT TCM8-1+

1:8 TRANSFORMER

LTC6416 Driving LTC2208 ADC

with 1:8 Transformer f

=140MHz,

= 130MHz, –1dBFS, PGA = 1

Summary of content (20 pages)

PAGE 1
LTC6416 2 GHz Low Noise Differential 16-Bit ADC Buffer DESCRIPTION FEATURES n n n n n n n n n n n n n n 2GHz –3dB Small Signal Bandwidth 300MHz ±0.1dB Bandwidth 1.8nV/√Hz Output Noise 46.25dBm Equivalent OIP3 at 140MHz 40.25dBm Equivalent OIP3 Up to 300MHz –81dBc/–72dBc HD2/HD3 at 140MHz, 2VP-P Out –84.5dBc IM3 at 140MHz, 2VP-P Out Composite –74dBc/–67.5dBc HD2/HD3 at 300MHz, 2VP-P Out –72.
PAGE 2
LTC6416 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Total Supply Voltage (V+ to GND)................................4V Input Current (CLLO, CLHI, VCM, IN+, IN–)...........±10mA Output Current (OUT+, OUT–) ...........................±22.5mA Operating Temperature Range (Note 2).... –40°C to 85°C Speciﬁed Temperature Range (Note 3) .... –40°C to 85°C Storage Temperature Range................... –65°C to 150°C Junction Temperature ...........................................
PAGE 3
LTC6416 3.6V ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V+ = 3.6V, GND = 0V, No RLOAD, CLOAD = 6pF. VCM = 1.25V, CLHI = V+, CLLO = 0V unless otherwise noted. VINCM is deﬁned as (IN+ + IN–)/2. VOUTCM is deﬁned as (OUT+ + OUT–)/2. VINDIFF is deﬁned as (IN+ – IN–). VOUTDIFF is deﬁned as (OUT+ – OUT–). See DC test circuit schematic.
PAGE 4
LTC6416 3.3V ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V+ = 3.3V, GND = 0V, No RLOAD, CLOAD = 6pF. VCM = 1.25V, CLHI = V+, CLLO = 0V unless otherwise noted. VINCM is deﬁned as (IN+ + IN–)/2. VOUTCM is deﬁned as (OUT+ + OUT–)/2. VINDIFF is deﬁned as (IN+ – IN–). VOUTDIFF is deﬁned as (OUT+ – OUT–). See DC test circuit schematic. SYMBOL PARAMETER CONDITIONS MIN TYP MAX –0.3 –0.4 –0.
PAGE 5
LTC6416 3.3V ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V+ = 3.3V, GND = 0V, No RLOAD, CLOAD = 6pF. VCM = 1.25V, CLHI = V+, CLLO = 0V unless otherwise noted. VINCM is deﬁned as (IN+ + IN–)/2. VOUTCM is deﬁned as (OUT+ + OUT–)/2. VINDIFF is deﬁned as (IN+ – IN–). VOUTDIFF is deﬁned as (OUT+ – OUT–). See DC test circuit schematic. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 2.23 2.
PAGE 6
LTC6416 AC ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V+ = 3.3V and 3.6V unless otherwise noted, GND = 0V, No RLOAD, CLOAD = 6pF. VCM = 1.25V, CLHI = VCC, CLLO = 0V unless otherwise noted. VINCM is deﬁned as (IN+ + IN–)/2. VOUTCM is deﬁned as (OUT+ + OUT–)/2. VINDIFF is deﬁned as (IN+ – IN–). VOUTDIFF is deﬁned as (OUT+ – OUT–). See DC test circuit schematic.
PAGE 7
LTC6416 TYPICAL PERFORMANCE CHARACTERISTICS 2 Differential Input Return Loss (S11) vs Frequency 0 V+ = 3.3V 0 V+ = 3.3V –5 –2 –10 –4 S11 (dB) –6 –8 –10 –15 –20 –25 –12 –30 –14 –16 10 100 1000 FREQUENCY (MHz) –35 10000 10 100 FREQUENCY (MHz) 6416 G01 –6 –7 –8 –9 –60 –70 –80 –70 –90 6416 G04 HD2 –80 –90 1000 100 FREQUENCY (MHz) –100 1000 V+ = 3.6V VCM = 1.
PAGE 8
LTC6416 TYPICAL PERFORMANCE CHARACTERISTICS Second and Third Harmonic Distortion vs Output Common Mode Voltage (140MHz) Second and Third Harmonic Distortion vs Output Common Mode Voltage (75MHz) –50 –60 –50 V+ = 3.6V RLOAD = 400Ω VOUT = 2VP-P DIFFERENTIAL Second and Third Harmonic Distortion vs Output Common Mode Voltage (250MHz) –50 V+ = 3.6V RLOAD = 400Ω VOUT = 2VP-P DIFFERENTIAL –60 –60 V+ = 3.6V RLOAD = 400Ω VOUT = 2VP-P DIFFERENTIAL HD3 –80 HD2 –90 –70 HD3 –80 HD2 –90 –100 1.05 1.10 1.15 1.
PAGE 9
LTC6416 TYPICAL PERFORMANCE CHARACTERISTICS Noise Figure and Input Referred Noise Voltage vs Frequency 50 SUPPLY CURRENT (mA) 40 35 30 25 20 15 10 5 0 0.5 1.0 1.5 2.0 2.5 3.0 SUPPLY VOLTAGE (V) 3.5 4.0 12 70 10 8 8 6 6 4 4 eN 10k Positive Overdrive Recovery (VCLHI Pin) IN+ 50 40 30 2 100k 1M 10M FREQUENCY (Hz) 100M 1G 10 0 0.
PAGE 10
LTC6416 TYPICAL PERFORMANCE CHARACTERISTICS V+ = 3.6V HD2 = –95dBc HD3 = –86dBc SFDR = 86dBc SNR = 74.6dBFS SEE FIGURE 5/TABLE 1 1:1 BALUN 3 2 0 20 30 40 FREQUENCY (MHz) 10 50 60 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 –120 –130 V+ = 3.6V HD2 = –99dBc HD3 = –91dBc SFDR = 91dBc SNR = 73dBFS SEE FIGURE 5/TABLE 1 1:1 BALUN 3 2 0 10 20 30 40 FREQUENCY (MHz) 50 6416 G22 0 10 AMPLITUDE (dBFS) AMPLITUDE (dBFS) 3 20 30 40 FREQUENCY (MHz) V+ = 3.6V HD2 = –85.6dBc HD3 = –95.
PAGE 11
LTC6416 PIN FUNCTIONS VCM (Pin 1): This pin sets the output common mode voltage seen at OUT+ and OUT– by driving IN+ and IN– through an internal buffer with a high output resistance of 6k. The VCM pin has a Thevenin equivalent resistance of approximately 3.8k and can be overdriven by an external voltage. If no voltage is applied to VCM, it will ﬂoat to a default voltage of approximately 1.25V on a 3.3V supply or 1.36V on a 3.6V supply.
PAGE 12
LTC6416 BLOCK DIAGRAM LTC6416 Simpliﬁed Schematic V+ 1 VCM R5 13.5k I1 R3 6k I11 x1 2 3 Q2 CLHI OUT+ Q4 Q3 IN+ 4 5 8 R2 9Ω Q1 R1 6k IN– 10 I13 Q12 R11 6k 7 R12 9Ω Q11 CLLO OUT– Q14 Q13 Q5 R6 2.
PAGE 13
LTC6416 APPLICATIONS INFORMATION Circuit Operation The LTC6416 is a low noise and low distortion fully differential unity-gain ADC driver with operation from DC to 2GHz (–3dB bandwidth), a differential input impedance of 12kΩ, and a differential output impedance of 18Ω. The LTC6416 is composed of a fully differential buffer with output common mode voltage control circuitry and high speed voltage-limiting clamps at the output.
PAGE 14
LTC6416 APPLICATIONS INFORMATION 0.1μF 3 1:4 8 OUT+ 100Ω 0.1μF • • 50Ω IN+ LTC6416 VIN + – 100Ω 0.1μF 4 IN– 7 OUT– 6416 F02 Figure 2. Input Termination for Differential 50Ω Input Impedance Using a 1:4 Balun 3 IN+ OUT+ 8 0.1μF 165Ω 1:1 0.1μF 50Ω LTC6416 IN– 7 OUT– • • 4 0.1μF 165Ω 6416 F03 Figure 3. Output Termination for Differential 400Ω Load Impedance Using a 1:1 Balun 3 IN+ 8 OUT+ 0.1μF 90.9Ω 4:1 0.1μF 50Ω LTC6416 IN– OUT– 7 • • 4 0.1μF 90.
PAGE 15
LTC6416 APPLICATIONS INFORMATION As seen in Table 1, suggested component values for the ﬁlter will change for differing IF frequencies. Table 1. INPUT FREQUENCY LTC6416 OUTPUT RESISTORS FILTERING CAPACITORS 30MHz 50Ω 5.6pF/6.8pF/5.6pF 70MHz 25Ω 5.6pF/6.8pF/5.6pF 140MHz 25Ω 1.5pF/1pF/1.5pF 250MHz 5Ω -/-/- Output Common Mode Adjustment The output common mode voltage is set by the VCM pin.
PAGE 16
LTC6416 APPLICATIONS INFORMATION Test Circuits Due to the fully differential design of the LTC6416 and its usefulness in applications both with and without ADCs, two test circuits are used to generate the information in this data sheet. Test circuit A is Demo Board DC1287A, a two-port demonstration circuit for the LTC6416. The board layout and the schematic are shown in Figures 6 and 7.
PAGE 17
LTC6416 APPLICATIONS INFORMATION Figure 8.
PAGE 18
J3 J2 C23 OPT C19 0.1μF C25 0.1μF C21 OPT 5 4 • T1 E2 E1 • CLLO E3 R18 OPT R17 OPT VCC 3 2 1 R12 OPT R11 OPT VCC TCM4−19+ CLHI VCM C26 0.1μF C18 0.1μF R10 OPT R8 OPT VCC CLK C27 0.1μF R14B 100Ω R14A 100Ω C13 0.1μF J4 5 4 3 2 1 C28 0.1μF CLLO IN− IN+ CLHI VCM GND OUT− OUT+ 6 7 8 9 10 VCC C29 0.1μF 5 4 • • 1 2 3 T2 MABA-007159-000000 11 GND V+ GND LTC6416CDDB R9 1k C16 2.2μF C9 0.1μF VDD C10 0.1μF GND VS 3.6V TO 20V R21 100Ω C24 1.
PAGE 19
LTC6416 PACKAGE DESCRIPTION DDB Package 10-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1722 Rev Ø) 0.64 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 6 0.40 ± 0.10 10 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.39 ±0.05 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 2.00 ±0.10 (2 SIDES) 0.75 ±0.05 0.64 ± 0.05 (2 SIDES) 5 0.25 ± 0.05 0 – 0.05 PIN 1 R = 0.20 OR 0.
PAGE 20
LTC6416 TYPICAL APPLICATION DC1257B Simpliﬁed Schematic with Suggested Output Termination for Driving an LTC2208 16-Bit ADC at 140MHz 3.6V 680pF T1 TCM4-19+ 4 50Ω 0.1μF 3 R36 100Ω 2 + – 6 2.2μF CLHI V+ IN+ VCM 25Ω 1 IN – 1.5pF OUT– GND GND C39 CLLO 0.01μF VCM AIN+ OUT+ LTC6416 R15 100Ω 3.3V 16 LTC2208 1pF DATA AIN– 25Ω 1.