LTC2207UK-14#TRPBF datasheet, PDF

FEATURES

■

LTC2207-14/LTC2206-14

14-Bit, 105Msps/80Msps

ADCs

DESCRIPTIO

The LTC

®

2207-14/LTC2206-14 are 105Msps/80Msps,

sampling 14-bit A/D converters designed for digitizing

high frequency, wide dynamic range signals up to input

frequencies of 700MHz. The input range of the ADC can

be optimized with the PGA front end.

The LTC2207-14/LTC2206-14 are perfect for demanding

communications applications, with AC performance that

includes 77.3dB SNR and 98dB spurious free dynamic

range (SFDR). Ultralow jitter of 80fs

RMS

allows under-

sampling of high input frequencies with excellent noise

performance. Maximum DC specs include ±1.5LSB INL,

±1LSB DNL (no missing codes) over temperature.

A separate output power supply allows the CMOS output

swing to range from 0.5V to 3.6V.

The ENC

+

and ENC

–

inputs may be driven differentially

or single-ended with a sine wave, PECL, LVDS, TTL or

CMOS inputs. An optional clock duty cycle stabilizer al-

lows high performance at full speed with a wide range of

clock duty cycles.

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

All other trademarks are the property of their respective owners. Patents Pending.

■

Sample Rate: 105Msps/80Msps

77.3dBFS Noise Floor

98dB SFDR

SFDR >82dB at 250MHz (1.5V

P-P

Input Range)

PGA Front End (2.25V

P-P

or 1.5V

P-P

Input Range)

700MHz Full Power Bandwidth S/H

Optional Internal Dither

Optional Data Output Randomizer

Single 3.3V Supply

Power Dissipation: 947mW/762mW

Optional Clock Duty Cycle Stabilizer

Out-of-Range Indicator

Pin Compatible Family

105Msps: LTC2207 (16-Bit), LTC2207-14 (14-Bit)

80Msps: LTC2206 (16-Bit), LTC2206-14 (14-Bit)

65Msps: LTC2205 (16-Bit), LTC2205-14 (14-Bit)

40Msps: LTC2204 (16-Bit)

25Msps: LTC2203 (16-Bit) Single-Ended Clock

10Msps: LTC2202 (16-Bit) Single-Ended Clock

48-Pin 7mm

×

7mm QFN Package

APPLICATIO S

■

Telecommunications

Receivers

Cellular Base Stations

Spectrum Analysis

Imaging Systems

ATE

TYPICAL APPLICATIO

3.3V

SENSE

V

CM

2.2µF

1.25V

COMMON MODE

BIAS VOLTAGE

INTERNAL ADC

REFERENCE

GENERATOR

OV

DD

0.5V TO 3.6V

0.1µF

OF

CLKOUT

+

CLKOUT

–

D13

•

D0

AMPLITUDE (dBFS)

3.3V

0.1µF

22076 TA01

AIN

+

ANALOG

INPUT

AIN

–

+

S/H

AMP

–

CLOCK/DUTY

CYCLE

CONTROL

ENC

+

ENC

–

14-BIT

PIPELINED

ADC CORE

CORRECTION

LOGIC AND

SHIFT REGISTER

OUTPUT

DRIVERS

OGND

V

DD

GND

PGA

SHDN

DITH

MODE

OE

RAND

0.1µF

ADC CONTROL INPUTS

U

LTC2207-14: 32K Point FFT,

f

IN

= 14.86MHz, –1dBFS,

PGA = 0, 105Msps

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

0

10

30

40

20

FREQUENCY (MHz)

50

22076 TA01b

220714614fa

1

LTC2207-14/LTC2206-14

ABSOLUTE MAXIMUM RATINGS

OV

DD

= V

DD

(Notes 1, 2)

PACKAGE/ORDER INFORMATION

48 GND

47 PGA

46 RAND

45 MODE

44 OE

43 OF

42 D13

41 D12

40 D11

39 D10

38 OGND

37 OV

DD

SENSE 1

V

CM

2

V

DD

3

V

DD

4

GND 5

AIN+ 6

AIN

–

7

GND 8

ENC

+

9

ENC

–

10

GND 11

V

DD

12

49

36 OV

DD

35 D9

34 D8

33 D7

32 D6

31 OGND

30 CLKOUT+

29 CLKOUT

–

28 D5

27 D4

26 D3

25 OV

DD

UK PACKAGE

48-LEAD (7mm

×

7mm) PLASTIC QFN

EXPOSED PAD IS GND (PIN 49)

MUST BE SOLDERED TO PCB BOARD

T

JMAX

= 125°C,

θ

JA

= 29°C/W

TOP VIEW

Supply Voltage (V

DD

) ................................... –0.3V to 4V

Digital Output Ground Voltage (OGND)........ –0.3V to 1V

Analog Input Voltage (Note 3) ......–0.3V to (V

DD

+ 0.3V)

Digital Input Voltage .....................–0.3V to (V

DD

+ 0.3V)

Digital Output Voltage ................ –0.3V to (OV

DD

+ 0.3V)

Power Dissipation............................................ 2000mW

Operating Temperature Range

LTC2207-14C/LTC2206-14C .................... 0°C to 70°C

LTC2207-14I/LTC2206-14I .................. –40°C to 85°C

Storage Temperature Range .................. –65°C to 150°C

Digital Output Supply Voltage (OV

DD

) .......... –0.3V to 4V

ORDER PART NUMBER

LTC2207CUK-14

LTC2206CUK-14

LTC2207IUK-14

LTC2206IUK-14

Order Options

Tape and Reel: Add #TR

Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking:

http://www.linear.com/leadfree/

Consult factory for parts speciﬁed with wider operating temperature ranges.

*The temperature grade is identiﬁed by a label on the shipping container.

CONVERTER CHARACTERISTICS

The

●

denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T

A

= 25°C. (Note 4)

CONDITIONS

Differential Analog Input (Note 5)

Differential Analog Input

(Note 6)

External Reference

Internal Reference

External Reference

●

PARAMETER

Integral Linearity Error

Differential Linearity Error

Offset Error

Offset Drift

Gain Error

Full-Scale Drift

Transition Noise

V

DD

13

V

DD

14

GND 15

SHDN 16

DITH 17

NC 18

NC 19

D0 20

D1 21

D2 22

OGND 23

OV

DD

24

UK PART MARKING*

LTC2207UK-14

LTC2206UK-14

LTC2207UK-14

LTC2206UK-14

MIN

TYP

±0.4

±0.1

±1

±10

±0.2

±30

±15

0.8

MAX

±1.5

±1

±10.3

±2.3

UNITS

LSB

mV

μV/

°C

%FS

ppm/°C

LSB

RMS

220714614fa

2

LTC2207-14/LTC2206-14

The

●

denotes the speciﬁcations which apply over the full operating temperature range, otherwise

speciﬁcations are at T

A

= 25°C. (Note 4)

SYMBOL

V

IN

V

IN, CM

I

IN

I

SENSE

I

MODE

C

IN

t

AP

t

JITTER

CMRR

BW-3dB

PARAMETER

Analog Input Range (A

IN+

–

A

IN–

)

Analog Input Common Mode

Analog Input Leakage Current

SENSE Input Leakage Current

MODE Pin Pull-Down Current to GND

Analog Input Capacitance

Sample-and-Hold

Acquisition Delay Time

Sample-and-Hold

Acquisition Delay Time Jitter

Analog Input

Common Mode Rejection Ratio

Full Power Bandwidth

CONDITIONS

3.135V ≤ V

DD

≤ 3.465V

Differential Input (Note 7)

0V ≤ A

IN+

,

A

IN–

≤ V

DD

(Note 8)

0V ≤ SENSE ≤ V

DD

(Note 9)

Sample Mode ENC

+

< ENC

–

Hold Mode ENC

+

> ENC

–

MIN

●

ANALOG INPUT

1

–1

–4

TYP

1.5 to 2.25

1.25

MAX

1.5

1

4

10

6.7

1.8

1

80

UNITS

V

P-P

V

µA

pF

ns

fs

RMS

dB

MHz

1V < (A

IN+

= A

IN–

) <1.5V

R

S

≤ 25Ω

80

700

DYNAMIC ACCURACY

SYMBOL PARAMETER

SNR

The

●

denotes the speciﬁcations which apply over the full operating temperature range,

otherwise speciﬁcations are at T

A

= 25°C. A

IN

= –1dBFS. (Note 4)

CONDITIONS

MIN

LTC2206-14

TYP

MAX

77.3

75.1

●

MIN

LC2207-14

TYP

77.3

75.1

MAX UNITS

dBFS

dBc

Signal-to-Noise Ratio 5MHz Input (2.25V Range, PGA = 0)

5MHz Input (1.5V Range, PGA = 1)

15MHz Input (2.25V Range, PGA = 0), T

A

= 25°C

15MHz Input (2.25V Range, PGA = 0)

15MHz Input (1.5V Range, PGA = 1)

70MHz Input (2.25V Range, PGA = 0)

70MHz Input (1.5V Range, PGA = 1)

140MHz Input (2.25V Range, PGA = 0)

140MHz Input (1.5V Range, PGA = 1), T

A

= 25°C

140MHz Input (1.5V Range, PGA = 1)

170MHz Input (2.25V Range, PGA = 0)

170MHz Input (1.5V Range, PGA = 1)

73.1

72.9

76

75.8

77.2

75

76.9

75

76.2

74.5

74.6

75.8

75.1

98

76

75.8

77.2

75

76.9

75

●

73.1

72.9

76.2

74.5

74.6

75.8

75.1

98

SFDR

Spurious Free

Dynamic Range

2

nd

or 3

rd

Harmonic

5MHz Input (2.25V Range, PGA = 0)

5MHz Input (1.5V Range, PGA = 1)

15MHz Input (2.25V Range, PGA = 0), T

A

= 25°C

15MHz Input (2.25V Range, PGA = 0)

15MHz Input (1.5V Range, PGA = 1)

70MHz Input (2.25V Range, PGA = 0)

70MHz Input (1.5V Range, PGA = 1)

140MHz Input (2.25V Range, PGA = 0)

140MHz Input (1.5V Range, PGA = 1), T

A

= 25°C

140MHz Input (1.5V Range, PGA = 1)

170MHz Input (2.25V Range, PGA = 0)

170MHz Input (1.5V Range, PGA = 1)

82

81

●

85

84

93

98

90

94

85

90

81

85

84

93

98

90

94

●

82

81

85

90

81

85

220714614fa

3

LTC2207-14/LTC2206-14

DYNAMIC ACCURACY

SYMBOL PARAMETER

SFDR

Spurious Free

Dynamic Range

4

th

Harmonic

or Higher

The

●

denotes the speciﬁcations which apply over the full operating temperature range,

otherwise speciﬁcations are at T

A

= 25°C. A

IN

= –1dBFS unless otherwise noted. (Note 4)

CONDITIONS

5MHz Input (2.25V Range, PGA = 0)

5MHz Input (1.5V Range, PGA = 1)

15MHz Input (2.25V Range, PGA = 0)

15MHz Input (1.5V Range, PGA = 1)

70MHz Input (2.25V Range, PGA = 0)

70MHz Input (1.5V Range, PGA = 1)

140MHz Input (2.25V Range, PGA = 0)

140MHz Input (1.5V Range, PGA = 1)

170MHz Input (2.25V Range, PGA = 0)

170MHz Input (1.5V Range, PGA = 1)

●

MIN

LTC2206-14

TYP

MAX

100

MIN

LC2207-14

TYP

100

MAX UNITS

dBc

dBFS

90

100

90

100

86.5

95

97

89

93

77

74.9

86.5

95

97

89

93

77

74.9

S/(N+D) Signal-to-Noise

Plus Distortion Ratio

5MHz Input (2.25V Range, PGA = 0)

5MHz Input (1.5V Range, PGA = 1)

15MHz Input (2.25V Range, PGA = 0), T

A

= 25°C

15MHz Input (2.25V Range, PGA = 0

15MHz Input (1.5V Range, PGA = 1)

70MHz Input (2.25V Range, PGA = 0)

70MHz Input (1.5V Range, PGA = 1)

140MHz Input (2.25V Range, PGA = 0)

140MHz Input (1.5V Range, PGA = 1), T

A

= 25°C

140MHz Input (1.5V Range, PGA = 1)

170MHz Input (2.25V Range, PGA = 0)

170MHz Input (1.5V Range, PGA = 1)

72.7

72.5

●

75.9

75.7

77.1

75.3

76.7

75

74.8

74.5

74.1

73.7

100

97

96

108

75.9

75.7

77.1

75.3

76.7

75

●

72.7

72.5

74.8

74.5

74.4

73.7

100

97

96

108

SFDR

Spurious Free

Dynamic Range

at –25dBFS

Dither “OFF”

5MHz Input (2.25V Range, PGA = 0)

5MHz Input (1.5V Range, PGA = 1)

15MHz Input (2.25V Range, PGA = 0)

15MHz Input (1.5V Range, PGA = 1)

70MHz Input (2.25V Range, PGA = 0)

70MHz Input (1.5V Range, PGA = 1)

140MHz Input (2.25V Range, PGA = 0)

140MHz Input (1.5V Range, PGA = 1)

170MHz Input (2.25V Range, PGA = 0)

170MHz Input (1.5V Range, PGA = 1)

SFDR

Spurious Free

Dynamic Range

at –25dBFS

Dither “ON”

5MHz Input (2.25V Range, PGA = 0)

5MHz Input (1.5V Range, PGA = 1)

15MHz Input (2.25V Range, PGA = 0)

15MHz Input (1.5V Range, PGA = 1)

70MHz Input (2.25V Range, PGA = 0)

70MHz Input (1.5V Range, PGA = 1)

140MHz Input (2.25V Range, PGA = 0)

140MHz Input (1.5V Range, PGA = 1)

170MHz Input (2.25V Range, PGA = 0)

170MHz Input (1.5V Range, PGA = 1)

●

95

107

102

100

95

107

102

100

220714614fa

4

LTC2207-14/LTC2206-14

The

●

denotes the speciﬁcations which apply over

the full operating temperature range, otherwise speciﬁcations are at T

A

= 25°C. (Note 4)

PARAMETER

V

CM

Output Voltage

V

CM

Output Tempco

V

CM

Line Regulation

V

CM

Output Resistance

CONDITIONS

I

OUT

= 0

I

OUT

= 0

3.135V ≤ V

DD

≤ 3.465V

–1mA ≤ | I

OUT

| ≤ 1mA

●

COMMON MODE BIAS CHARACTERISTICS

MIN

1.15

TYP

1.25

40

1

2

MAX

1.35

UNITS

V

ppm/°C

mV/ V

Ω

The

●

denotes the speciﬁcations which apply over the

full operating temperature range, otherwise speciﬁcations are at T

A

= 25°C. (Note 4)

SYMBOL

PARAMETER

ENCODE INPUTS (ENC

+

, ENC

–

)

V

ID

Differential Input Voltage

V

ICM

Common Mode Input Voltage

R

IN

Input Resistance

C

IN

Input Capacitance

LOGIC INPUTS (DITH, PGA, SHDN, RAND)

V

IH

High Level Input Voltage

V

IL

Low Level Input Voltage

I

IN

Input Current

C

IN

Input Capacitance

LOGIC OUTPUTS

OV

DD

= 3.3V

V

OH

High Level Output Voltage

V

OL

I

SOURCE

I

SINK

OV

DD

= 2.5V

V

OH

V

OL

OV

DD

= 1.8V

V

OH

V

OL

Low Level Output Voltage

Output Source Current

Output Sink Current

High Level Output Voltage

Low Level Output Voltage

High Level Output Voltage

Low Level Output Voltage

CONDITIONS

(Note 7)

Internally Set

Externally Set (Note 7)

(See Figure 2)

(Note 7)

V

DD

= 3.3V

V

DD

= 3.3V

V

IN

= 0V to V

DD

(Note 7)

●

DIGITAL INPUTS AND DIGITAL OUTPUTS

MIN

0.2

TYP

MAX

UNITS

V

1.6

1.4

6

3

2

0.8

±10

1.5

3.0

k

Ω

pF

V

µA

pF

V

DD

= 3.3V

V

DD

= 3.3V

V

OUT

= 0V

V

OUT

= 3.3V

V

DD

= 3.3V

V

DD

= 3.3V

V

DD

= 3.3V

V

DD

= 3.3V

I

O

= –10µA

I

O

= –200µA

I

O

= 160µA

I

O

= 1.6mA

●

3.1

3.299

3.29

0.01

0.10

–50

50

2.49

0.1

1.79

0.1

0.4

V

mA

V

I

O

= –200µA

I

O

= 1.60mA

I

O

= –200µA

I

O

= 1.60mA

The

●

denotes the speciﬁcations which apply over the full operating temperature

range, otherwise speciﬁcations are at T

A

= 25°C. A

IN

= –1dBFS. (Note 4)

SYMBOL PARAMETER

V

DD

P

SHDN

OV

DD

I

VDD

P

DIS

Analog Supply Voltage

Shutdown Power

Output Supply Voltage

Analog Supply Current

Power Dissipation

DC Input

SHDN = V

DD

●

POWER REQUIREMENTS

CONDITIONS

●

MIN

3.135

0.5

LTC2206-14

TYP

3.3

0.2

MAX

3.465

3.6

MIN

3.135

0.5

LTC2207-14

TYP

3.3

0.2

MAX

3.465

3.6

UNITS

V

mW

V

mA

mW

231

762

275

908

287

947

350

1155

220714614fa

5

Parameter Name	Attribute value
Maker	Linear ( ADI )
Parts packaging code	QFN
package instruction	HVQCCN,
Contacts	48
Reach Compliance Code	unknown
Maximum analog input voltage	2.25 V
Minimum analog input voltage	-2.25 V
Converter type	ADC, PROPRIETARY METHOD
JESD-30 code	S-PQCC-N48
length	7 mm
Maximum linear error (EL)	0.0092%
Number of analog input channels	1
Number of digits	14
Number of functions	1
Number of terminals	48
Maximum operating temperature	70 °C
Minimum operating temperature
Output bit code	OFFSET BINARY, 2\'S COMPLEMENT BINARY
Output format	PARALLEL, WORD
Package body material	PLASTIC/EPOXY
encapsulated code	HVQCCN
Package shape	SQUARE
Package form	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE
Certification status	Not Qualified
Sampling rate	105 MHz
Sample and hold/Track and hold	SAMPLE
Maximum seat height	0.8 mm
Nominal supply voltage	3.3 V
surface mount	YES
technology	CMOS
Temperature level	COMMERCIAL
Terminal form	NO LEAD
Terminal pitch	0.5 mm
Terminal location	QUAD
width	7 mm

	LTC2207UK-14#TRPBF	LTC2207UK-14#PBF	LTC2207UK-14#TR	LTC2206UK-14#PBF	LTC2206UK-14#TRPBF	LTC2206UK-14#TR
Description	IC PROPRIETARY METHOD ADC, PQCC48, 7 X 7 MM, LEAD FREE, PLASTIC, MO-220WKKD-2, QFN-48, Analog to Digital Converter	IC PROPRIETARY METHOD ADC, PQCC48, 7 X 7 MM, LEAD FREE, PLASTIC, MO-220WKKD-2, QFN-48, Analog to Digital Converter	IC PROPRIETARY METHOD ADC, PQCC48, 7 X 7 MM, PLASTIC, MO-220WKKD-2, QFN-48, Analog to Digital Converter	IC PROPRIETARY METHOD ADC, PQCC48, 7 X 7 MM, LEAD FREE, PLASTIC, MO-220WKKD-2, QFN-48, Analog to Digital Converter	IC PROPRIETARY METHOD ADC, PQCC48, 7 X 7 MM, LEAD FREE, PLASTIC, MO-220WKKD-2, QFN-48, Analog to Digital Converter	IC PROPRIETARY METHOD ADC, PQCC48, 7 X 7 MM, PLASTIC, MO-220WKKD-2, QFN-48, Analog to Digital Converter
Parts packaging code	QFN	QFN	QFN	QFN	QFN	QFN
package instruction	HVQCCN,	HVQCCN,	HVQCCN,	HVQCCN,	HVQCCN,	HVQCCN,
Contacts	48	48	48	48	48	48
Reach Compliance Code	unknown	unknown	unknown	unknown	unknown	unknown
Maximum analog input voltage	2.25 V	2.25 V	2.25 V	2.25 V	2.25 V	2.25 V
Minimum analog input voltage	-2.25 V	-2.25 V	-2.25 V	-2.25 V	-2.25 V	-2.25 V
Converter type	ADC, PROPRIETARY METHOD	ADC, PROPRIETARY METHOD	ADC, PROPRIETARY METHOD	ADC, PROPRIETARY METHOD	ADC, PROPRIETARY METHOD	ADC, PROPRIETARY METHOD
JESD-30 code	S-PQCC-N48	S-PQCC-N48	S-PQCC-N48	S-PQCC-N48	S-PQCC-N48	S-PQCC-N48
length	7 mm	7 mm	7 mm	7 mm	7 mm	7 mm
Maximum linear error (EL)	0.0092%	0.0092%	0.0092%	0.0092%	0.0092%	0.0092%
Number of analog input channels	1	1	1	1	1	1
Number of digits	14	14	14	14	14	14
Number of functions	1	1	1	1	1	1
Number of terminals	48	48	48	48	48	48
Maximum operating temperature	70 °C	70 °C	70 °C	70 °C	70 °C	70 °C
Output bit code	OFFSET BINARY, 2\'S COMPLEMENT BINARY	OFFSET BINARY, 2'S COMPLEMENT BINARY	OFFSET BINARY, 2\'S COMPLEMENT BINARY	OFFSET BINARY, 2\'S COMPLEMENT BINARY	OFFSET BINARY, 2\'S COMPLEMENT BINARY	OFFSET BINARY, 2\'S COMPLEMENT BINARY
Output format	PARALLEL, WORD	PARALLEL, WORD	PARALLEL, WORD	PARALLEL, WORD	PARALLEL, WORD	PARALLEL, WORD
Package body material	PLASTIC/EPOXY	PLASTIC/EPOXY	PLASTIC/EPOXY	PLASTIC/EPOXY	PLASTIC/EPOXY	PLASTIC/EPOXY
encapsulated code	HVQCCN	HVQCCN	HVQCCN	HVQCCN	HVQCCN	HVQCCN
Package shape	SQUARE	SQUARE	SQUARE	SQUARE	SQUARE	SQUARE
Package form	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE	CHIP CARRIER, HEAT SINK/SLUG, VERY THIN PROFILE
Certification status	Not Qualified	Not Qualified	Not Qualified	Not Qualified	Not Qualified	Not Qualified
Sampling rate	105 MHz	105 MHz	105 MHz	80 MHz	80 MHz	80 MHz
Sample and hold/Track and hold	SAMPLE	SAMPLE	SAMPLE	SAMPLE	SAMPLE	SAMPLE
Maximum seat height	0.8 mm	0.8 mm	0.8 mm	0.8 mm	0.8 mm	0.8 mm
Nominal supply voltage	3.3 V	3.3 V	3.3 V	3.3 V	3.3 V	3.3 V
surface mount	YES	YES	YES	YES	YES	YES
technology	CMOS	CMOS	CMOS	CMOS	CMOS	CMOS
Temperature level	COMMERCIAL	COMMERCIAL	COMMERCIAL	COMMERCIAL	COMMERCIAL	COMMERCIAL
Terminal form	NO LEAD	NO LEAD	NO LEAD	NO LEAD	NO LEAD	NO LEAD
Terminal pitch	0.5 mm	0.5 mm	0.5 mm	0.5 mm	0.5 mm	0.5 mm
Terminal location	QUAD	QUAD	QUAD	QUAD	QUAD	QUAD
width	7 mm	7 mm	7 mm	7 mm	7 mm	7 mm
Maker	Linear ( ADI )	-	Linear ( ADI )	Linear ( ADI )	Linear ( ADI )	Linear ( ADI )

LTC2207UK-14#TRPBF

LTC2207UK-14#TRPBF Overview

LTC2207UK-14#TRPBF Parametric

Preview

LTC2207UK-14#TRPBF Related Products

Recommended Resources