MAX261BENG 查看數據表（PDF） - Maxim Integrated

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MAX261BENG

Microprocessor Programmable Universal Active Filters

Maxim Integrated 

Microprocessor Programmable

Universal Active Filters

SCN = SWITCH-CAPACITOR NETWORK

SCN

IN

SCN

-

+

S1 S2 S3

S1

-

+Σ

-

S2

S-H

SAMPLE-HOLD

MAX260 ONLY

∫

∫

N/HP/AP

BP

LP

MODE

SELECT

M0

M1

SCN

S3

SCN

Q0–Q6

(TABLE 3)

F0–F5

(TABLE 2)

Figure 1. Filter Block Diagram (One Second-Order Section)

Introduction

Each MAX260/MAX261/MAX262 contains two second-

order switched-capacitor active filters. Figure 1 shows

the filter's state variable topology, employed with two

cascaded integrators and one summing amplifier. The

MAX261 and MAX262 also contain an uncommitted

amplifier. On-chip switches and capacitors provide

feedback to-control each filter section's f0 and Q.

Internal capacitor ratios are primarily responsible for

the accuracy of these parameters. Although these

switched-capacitor networks (SCN) are in fact sampled

systems, their behavior very closely matches that of

continuous filters, such as RC active filters. The ratio of

the clock frequency to the filter center frequency

(fCLK/f0) is kept large so that ideal second-order state-

variable response is maintained.

The MAX262 uses a lower range of sampling (fCLK/f0)

ratios than the MAX260 or MAX261 to allow higher

operating f0 frequencies and signal bandwidths. These

reduced sample rates result in somewhat more devia-

tion from ideal continuous filter parameters than with

the MAX260/MAX261. However, these differences can

be compensated using Figure 20 (see Application

Hints) or Maxim's filter design software.

The MAX260 employs auto-zero circuitry not included

in the MAX261 or MAX262. This provides improved DC

characteristics, and improved low-frequency perform-

ance at the expense of high-end f0 and signal band-

width. The N/HP/AP outputs of the MAX260 are internal-

ly sample-and-held as a result of its auto-zero

operation. Signal swing at this output is somewhat

reduced as a result (MAX260 only). See Table 1 for

bandwidth comparisons of the three filters.

Maxim also provides design programs that aid in con-

verting filter response specifications into the f0 and Q

program codes used by the MAX260 series devices.

This software also precompensates f0 and Q when low

sample rates are used.

It is important to note that, in all MAX260 series filters,

the filter's internal sample rate is one half the input

clock rate (CLKA or CLKB) due to an internal division

by two. All clock-related data, tables, and other dis-

cussions in this data sheet refer to the frequency at the

CLKA or CLKB input, i.e., twice the internal sample rate,

unless specifically stated otherwise.

Quick Look Design Procedure

The MAX260, MAX261, and MAX262, with Maxim's filter

design software, greatly simplify the design procedures

for many active filters. Most designs can be realized

using a three-step process described in this section. If

the design software is not used, or if the filter complexi-

ty is beyond the scope of this section, refer to the

remainder of this data sheet for more detailed applica-

tions and design information.

_______________________________________________________________________________________ 7

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