ML4622CP Просмотр технического описания (PDF) - Micro Linear Corporation

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ML4622CP

Fiber Optic Data Quantizer

Micro Linear Corporation 

ML4622, ML4624

FUNCTIONAL DESCRIPTION

AMPLIFIER

The ML4622, ML4624 have an adjustable Bandwidth

limiting amplifier. Maximum sensitivity is achieved

through the use of a DC restoration feedback loop and

AC coupling the input. When AC coupled, the input DC

bias voltage is set by an on-chip network at about 1.7V.

These coupling capacitors, in conjunction with the input

impedance of the amplifier, establish a high pass filter

with a 3dB corner frequency, fL, at

fL =

1

2π 1600 C

(1)

Since the amplifier has a differential input, two capacitors

of equal value are required. If the signal driving the input

is single ended, one of the coupling capacitors can be tied

to VCC as shown in figure 1.

CF1 and CF2 create a low pass filter with the corner

frequency determined by the following equation

fH =

1

2π 800(C + 4pF)

(2)

VOUT+

VOS

VOUT–

Figure 2.

The above equation applies when a single capacitor is

tied between CF1 and CF2. When using two capacitors of

equal value (Cap1 from CF1 to VCC, Cap2 from CF2 to

VCC) the value derived for C should be doubled.

Although the input is AC coupled, the offset voltage

within the amplifier will be present at the amplifier’s

output. This is represented by VOS in figure 2. In order to

reduce this error a DC feedback loop is incorporated. This

negative feedback loop nulls the offset voltage, forcing

VOS to be zero. Although the capacitor on VDC is non-

+VRF

0.1

10Ω

–VRF

6

FIBER OPTIC CABLE

0.01 VIN–

2 0.01 VIN+

HFBR 1

2416 4

5

8

37

0.1VDC

–VRF

VREF

BIAS

VTHADJ

5pF

CF1

CF2

ECL+ ECL–

AMP

ECL

CMP

∫

REF

THRESH

GEN

LINK DETECT

TTL

CMP

TTL OUT

CMP ENABLE

TTL LINK MON

VCC GND VCC

TTL* TTL

CTIMER

0.05

GND

L1

4.7µH

+5V

0.1

+

4.7

+

4.7

0.1

+VRF

–VRF

L2

4.7µH

*ML4624 ONLY

Note:

If TTL OUT is used, tie GND TTL to unfiltered ground and remove L1. If TTL OUT and ECL outputs are both used, add 3K pulldown resistors at

ECL outputs.

Figure 1. The ML4622, ML4624 Configured for 20MHz Bandwidth

6

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