MAX1448 查看數據表（PDF） - Maxim Integrated

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MAX1448

10-Bit, 80Msps, Single 3.0V, Low-Power ADC with Internal Reference

Maxim Integrated 

10-Bit, 80Msps, Single 3.0V, Low-Power

ADC with Internal Reference

_______________Detailed Description

The MAX1448 uses a 10-stage, fully differential,

pipelined architecture (Figure 1) that allows for high-

speed conversion while minimizing power consump-

tion. Each sample moves through a pipeline stage

every half clock-cycle. Counting the delay through the

output latch, the clock-cycle latency is 5.5.

A 1.5-bit (2-comparator) flash ADC converts the held

input voltage into a digital code. The following digital-

to-analog converter (DAC) converts the digitized result

back into an analog voltage, which is then subtracted

from the original held input signal. The resulting error

signal is then multiplied by two, and the product is

passed along to the next pipeline stage where the

process is repeated. Each stage provides a 1-bit reso-

lution. Digital error correction compensates for ADC

comparator offsets in each pipeline stage and ensures

no missing codes.

Input Track-and-Hold Circuit

Figure 2 displays a simplified functional diagram of the

input track-and-hold (T/H) circuit in both track and hold

mode. In track mode, switches S1, S2a, S2b, S4a, S4b,

S5a, and S5b are closed. The fully differential circuit

samples the input signal onto the two capacitors (C2a

and C2b) through S4a and S4b. S2a and S2b set the

common mode for the amplifier input and open simulta-

MDAC

VIN

T/H

Σ

x2

VOUT

FLASH

ADC

DAC

1.5 BITS

neously with S1, sampling the input waveform. S4a and

S4b are then opened before S3a and S3b connect

capacitors C1a and C1b to the amplifier output, and

S4c is closed. The resulting differential voltage is held

on C2a and C2b. The amplifier is used to charge C1a

and C1b to the same values originally held on C2a and

C2b. This value is then presented to the first-stage

quantizer and isolates the pipeline from the fast-chang-

ing input. The wide-input-bandwidth T/H amplifier

allows the MAX1448 to track and sample/hold analog

inputs of high frequencies beyond Nyquist. Analog

inputs (IN+ and IN-) can be driven either differentially

or single-ended. It is recommended to match the

impedance of IN+ and IN- and set the common-mode

voltage to midsupply (VDD/2) for optimum performance.

Analog Input and Reference Configuration

The MAX1448 full-scale range is determined by the

internally generated voltage difference between REFP

(VDD/2 + VREFIN/4) and REFN (VDD/2 - VREFIN/4). The

ADC’s full-scale range is user-adjustable through the

REFIN pin, which provides a high input impedance for

this purpose. REFOUT, REFP, COM (VDD/2), and REFN

are internally buffered, low-impedance outputs.

INTERNAL

BIAS

S2a

COM

S5a

C1a

S3a

S4a

IN+

OUT

C2a

S4c

S1

IN-

S4b

C2b

OUT

C1b

VIN

STAGE 1

STAGE 2

STAGE 10

DIGITAL CORRECTION LOGIC

10

D9–D0

VIN = INPUT VOLTAGE BETWEEN

IN+ AND IN- (DIFFERENTIAL OR SINGLE ENDED)

S3b

S2b

S5b

INTERNAL

COM

BIAS

TRACK TRACK

CLK

HOLD

HOLD

INTERNAL

NON OVERLAPPING

CLOCK SIGNALS

Figure 1. Pipelined Architecture—Stage Blocks

Figure 2. Internal Track-and-Hold Circuit

______________________________________________________________________________________ 11

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