LTC2246H Schematic - Linear Technology

LTC2246H Schematic ( PDF Datasheet ) - Linear Technology

Teilenummer	LTC2246H
Beschreibung	ADC
Hersteller	Linear Technology
Logo
Gesamt 18 Seiten FEATURES n Sample Rate: 25Msps n –40°C to 125°C Operation n Single 3V Supply (2.8V to 3.5V) n Low Power: 75mW n 74.5dB SNR n 90dB SFDR n No Missing Codes n Flexible Input: 1VP-P to 2VP-P Range n 575MHz Full Power Bandwidth S/H n Clock Duty Cycle Stabilizer n Shutdown and Nap Modes n Pin Compatible Family LTC2246H (14-Bit), LTC2226H (12-Bit) n 48-Pin (7mm × 7mm) LQFP Package APPLICATIONS n Automotive n Industrial n Wireless and Wired Broadband Communication LTC2246H 14-Bit, 25Msps 125°C ADC In LQFP DESCRIPTION The LTC®2246H is a 14-bit 25Msps, low power 3V A/D converter designed for digitizing high frequency, wide dynamic range signals. The LTC2246H is perfect for demanding imaging and communications applications with AC performance that includes 74.5dB SNR and 90dB SFDR. DC specs include ±1LSB INL (typ), ±0.5LSB DNL (typ) and no missing codes over temperature. The transition noise is a low 1LSBRMS. A single 3V supply allows low power operation. A separate output supply allows the outputs to drive 0.5V to 3.6V logic. A single-ended CLK input controls converter operation. An optional clock duty cycle stabilizer allows high performance at full speed for a wide range of clock duty cycles. 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. TYPICAL APPLICATION REFH REFL ANALOG INPUT FLEXIBLE REFERENCE + INPUT S/H – CLOCK/DUTY CYCLE CONTROL CLK 14-BIT PIPELINED ADC CORE CORRECTION LOGIC OUTPUT DRIVERS OVDD D13 • • • D0 OGND 2246H TA01 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 0 Typical INL, 2V Range 4096 8192 CODE 12288 16384 2246H TA01b 2246hfb 1 LTC2246H TYPICAL PERFORMANCE CHARACTERISTICS 8192 Point 2-Tone FFT, fIN = 10.9MHz and 13.8MHz, –1dB, 2V Range, 25Msps 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 –120 0 2 4 6 8 10 12 FREQUENCY (MHz) 2246H G07 Grounded Input Histogram, 25Msps 25000 22016 20000 18803 15000 13373 10000 6919 5000 3227 43 853 0 278 8179 8180 8181 8182 8183 8184 8185 8186 CODE 2246H G08 SFDR vs Input Frequency, –1dB, 2V Range, 25Msps 100 95 90 85 80 75 70 65 0 50 100 150 200 INPUT FREQUENCY (MHz) 2246H G10 SNR and SFDR vs Sample Rate, 2V Range, fIN = 5MHz, –1dB 110 100 SFDR 90 80 SNR 70 60 0 10 20 30 40 50 SAMPLE RATE (Msps) 2246H G11 SFDR vs Input Level, fIN = 5MHz, 2V Range, 25Msps 120 110 100 dBFS 90 80 dBc 70 60 90dBc SFDR REFERENCE LINE 50 40 30 20 –60 –50 –40 –30 –20 –10 0 INPUT LEVEL (dBFS) 2246H G13 IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB 35 30 2V RANGE 25 1V RANGE 20 15 0 5 10 15 20 25 30 35 SAMPLE RATE (Msps) 2246H G14 6 SNR vs Input Frequency, –1dB, 2V Range, 25Msps 75 74 73 72 71 70 0 50 100 150 200 INPUT FREQUENCY (MHz) 2246H G09 SNR vs Input Level, fIN = 5MHz, 2V Range, –1dB 80 70 dBFS 60 50 dBc 40 30 20 10 0 –60 –50 –40 –30 –20 –10 0 INPUT LEVEL (dBFS) 2246H G12 IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.8V 3 2 1 0 0 5 10 15 20 25 30 35 SAMPLE RATE (Msps) 2246H G15 2246hfb 6 Page LTC2246H APPLICATIONS INFORMATION Input Drive Impedance As with all high performance, high speed ADCs, the dy- namic performance of the LTC2246H can be inﬂuenced by the input drive circuitry, particularly the second and third harmonics. Source impedance and reactance can inﬂuence SFDR. At the falling edge of CLK, the sample-and-hold circuit will connect the 4pF sampling capacitor to the input pin and start the sampling period. The sampling period ends when CLK rises, holding the sampled input on the sampling capacitor. Ideally the input circuitry should be fast enough to fully charge the sampling capacitor during the sampling period 1/(2FENCODE); however, this is not always possible and the incomplete settling may degrade the SFDR. The sampling glitch has been designed to be as linear as possible to minimize the effects of incomplete settling. For the best performance, it is recommended to have a source impedance of 100Ω or less for each input. The source impedance should be matched for the differential inputs. Poor matching will result in higher even order harmonics, especially the second. Input Drive Circuits Figure 3 shows the LTC2246H being driven by an RF transformer with a center tapped secondary. The secondary center tap is DC biased with VCM, setting the ADC input signal at its optimum DC level. Terminating on the trans- former secondary is desirable, as this provides a common mode path for charging glitches caused by the sample and ANALOG INPUT 0.1μF T1 1:1 25Ω 25Ω 0.1μF 25Ω 25Ω T1 = MA/COM ETC1-1T RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE VCM 2.2μF AIN+ LTC2246H 12pF AIN– 2246H F03 Figure 3. Single-Ended to Differential Conversion Using a Transformer hold. Figure 3 shows a 1:1 turns ratio transformer. Other turns ratios can be used if the source impedance seen by the ADC does not exceed 100Ω for each ADC input. A disadvantage of using a transformer is the loss of low frequency response. Most small RF transformers have poor performance at frequencies below 1MHz. Figure 4 demonstrates the use of a differential ampliﬁer to convert a single ended input signal into a differential input signal. The advantage of this method is that it provides low frequency input response; however, the limited gain bandwidth of most op amps will limit the SFDR at high input frequencies. Figure 5 shows a single-ended input circuit. The impedance seen by the analog inputs should be matched. This circuit is not recommended if low distortion is required. The 25Ω resistors and 12pF capacitor on the analog inputs serve two purposes: isolating the drive circuitry from the sample-and-hold charging glitches and limiting the wideband noise at the converter input. ANALOG INPUT HIGH SPEED DIFFERENTIAL AMPLIFIER 25Ω ++ CM –– 25Ω VCM 2.2μF AIN+ LTC2246H 12pF AIN– 2246H F04 Figure 4. Differential Drive with an Ampliﬁer ANALOG INPUT 0.1μF 1k 1k 25Ω VCM 2.2μF AIN+ LTC2246H 12pF 25Ω 0.1μF AIN– 2246H F05 Figure 5. Single-Ended Drive 12 2246hfb 12 Page
Seiten	Gesamt 18 Seiten
PDF Download	[ LTC2246H Schematic.PDF ]

Link teilen

Besondere Datenblatt

Teilenummer	Beschreibung	Hersteller
LTC2246	(LTC2246 - LTC2248) 65/40/25Msps Low Power 3V ADCs	Linear Technology
LTC2246H	ADC	Linear Technology

Teilenummer	Beschreibung	Hersteller
CD40175BC	Hex D-Type Flip-Flop / Quad D-Type Flip-Flop.	Fairchild Semiconductor
KTD1146	EPITAXIAL PLANAR NPN TRANSISTOR.	KEC

www.Datenblatt-PDF.com | 2020 | Kontakt | Suche