LMH6624 datasheet(17/20 Pages) NSC

17 / 20 page

Application Section (Continued)

HIGH-GAIN SALLEN-KEY ACTIVE FILTERS

The LMH6624/LMH6626 are well suited for high gain Sallen-

Key type of active filters. Figure 12 shows the 2

nd order

Sallen-Key low pass filter topology. Using component predis-

tortion methods discussed in OA-21 enables the proper

selection of components for these high-frequency filters.

LOW NOISE MAGNETIC MEDIA EQUALIZER

The LMH6624/LMH6626 implement a high-performance low

noise equalizer for such application as magnetic tape chan-

nels as shown in Figure 13. The circuit combines an integra-

tor with a bandpass filter to produce the low noise equaliza-

tion. The circuit’s simulated frequency response is illustrated

in Figure 14.

LAYOUT CONSIDERATION

National Semiconductor suggests the copper patterns on the

evaluation boards listed below as a guide for high frequency

layout. These boards are also useful as an aid in device

testing and characterization. As is the case with all high-

speed amplifiers, accepted-practice RF design technique on

the PCB layout is mandatory. Generally, a good high fre-

quency layout exhibits a separation of power supply and

ground traces from the inverting input and output pins. Para-

sitic capacitances between these nodes and ground may

cause frequency response peaking and possible circuit os-

cillations (see Application Note OA-15 for more information).

Use high quality chip capacitors with values in the range of

1000pF to 0.1F for power supply bypassing. One terminal of

each chip capacitor is connected to the ground plane and the

other terminal is connected to a point that is as close as

possible to each supply pin as allowed by the manufacturer’s

design rules. In addition, connect a tantalum capacitor with a

value between 4.7µF and 10µF in parallel with the chip

capacitor. Signal lines connecting the feedback and gain

resistors should be as short as possible to minimize induc-

tance and microstrip line effect. Place input and output ter-

mination resistors as close as possible to the input/output

pins. Traces greater than 1 inch in length should be imped-

ance matched to the corresponding load termination.

20058929

FIGURE 11. Low Noise Integrator

20058930

FIGURE 12. Sallen-Key Active Filter Topology

20058931

FIGURE 13. Noise Magnetic Media Equalizer

20058932

FIGURE 14. Equalizer Frequency Response

LMH6624 Datasheet(PDF) 17 Page - National Semiconductor (TI)

LMH6624 Datasheet(HTML) 17 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL