OPA650 datasheet(11/24 Pages) TI2

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Differential ADC Driver

Bandpass Filter

-5

-10

-15

-20

-25

-30

-35

-40

10k

100k

10M

100M

Frequency(Hz)

1/2

OPA2652

1/2

OPA2652

24.9W

143W

140W

2.10kW

1.0nF

+5V

-5V

2.2nF

1.30kW

24.9W

200W

107W

225W

20.0W

158W

150pF

12pF

2.7nF

+5V

-5V

180pF

100W

100pF

1%Resistors

5%Capacitors

18pF

OUT

OPA2652

SBOS125A – JUNE 2000 – REVISED MAY 2006

The circuit on the front page shows an OPA2652

driving the ADS807 analog-to-digital converter (ADC)

differentially, at a gain of +2V/V. The outputs are

AC-coupled to the converter to adjust for the

difference in supply voltages. The 133

Ω resistors at

the noninverting inputs minimize DC offset errors.

The

differential

topology

minimizes

even-order

distortion

products,

such

second-harmonic

distortion.

Figure 31 shows a single OPA2652 implementing a

sixth-order bandpass filter. This filter cascades two

second-order Sallen-Key sections with transmission

Figure 30. Nominal Filter Response

zeros, and a double real pole section. It has 0.3dB of

ripple, –3dB frequencies of 450kHz and 11MHz, and

–23dB frequencies of 315kHz and 16MHz. The

20.0

Ω resistor isolates the first OPA2652 output from

capacitive

This

configuration

improves

stability with minimal impact on the filter response.

Figure 30 shows the nominal response simulated by

SPICE.

Figure 31. Bandpass Filter

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