THS6002

DUAL DIFFERENTIAL LINE DRIVERS AND RECEIVERS

SLOS202D– JANUARY 1998– REVISED JULY 1999

37

POST OFFICE BOX 655303

APPLICATION INFORMATION

general configurations (continued)

VI

VO

C1

+

–

RG

RF

R1

f

–3dB +

1

2

pR1C1

V

O

V

I

+ 1 )

R

F

R

G

1

1

) sR1C1

Figure 61. Single-Pole Low-Pass Filter

If a multiple pole filter is required, the use of a Sallen-Key filter can work very well with CFB amplifiers. This is

because the filtering elements are not in the negative feedback loop and stability is not compromised. Because

of their high slew-rates and high bandwidths, CFB amplifiers can create very accurate signals and help minimize

distortion. An example is shown in Figure 62.

VI

C2

R2

R1

C1

RF

RG

R1 = R2 = R

C1 = C2 = C

Q = Peaking Factor

(Butterworth Q = 0.707)

(

=

1

Q

2 –

)

RG

RF

_

+

f

–3dB +

1

2

pRC

Figure 62. 2-Pole Low-Pass Sallen-Key Filter

There are two simple ways to create an integrator with a CFB amplifier. The first one shown in Figure 63 adds

a resistor in series with the capacitor. This is acceptable because at high frequencies, the resistor is dominant

and the feedback impedance never drops below the resistor value. The second one shown in Figure 64 uses

positive feedback to create the integration. Caution is advised because oscillations can occur because of the

positive feedback.

+

–

C1

RF

RG

VO

VI

THS6002

V

O

V

I

+

R

F

R

G

S

) 1

R

F

C1

S

Figure 63. Inverting CFB Integrator