H

d

(f) +

K

–

f

FSF x fc

2

)

1

Q

jf

FSF x fc )

1

x

Rt

2R4 ) Rt

1 )

j2

πfR4RtC3

2R4 ) Rt

Where K +

R2

R1

FSF x fc +

1

2

π 2 x R2R3C1C2

and Q +

2 x R2R3C1C2

R3C1 ) R2C1 ) KR3C1

FSF +

Re

2

and Q +

2

2Re

FSF x fc +

1

2

πRC 2 x mn

and Q +

2 x mn

1 ) m(1 ) K)

THEORY OF OPERATION

_

+

Differential Amplifier

_

+

_

+

THS415x

Fully differential Amplifier

THS4150

THS4151

The transfer function for this filter circuit is:

K sets the pass band gain, fc is the cutoff frequency for the filter, FSF is a frequency-scaling factor, and Q is the

quality factor.

where Re is the real part, and Im is the imaginary part of the complex pole pair. Setting R2 = R, R3 = mR, C1 =

C, and C2 = nC results in:

Start by determining the ratios, m and n, required for the gain and Q of the filter type being designed, then select

C and calculate R for the desired fc.

PRINCIPLES OF OPERATION

The THS415x is a fully differential amplifier. Differential amplifiers are typically differential in/single out, whereas

fully differential amplifiers are differential in/differential out.

Figure 36. Differential Amplifier Versus a Fully Differential Amplifier

To understand the THS415x fully differential amplifiers, the definition for the pinouts of the amplifier are provided.

16

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