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Positive Voltage Output Circuit

GND

-2.5V

+2.5VReference

OPA277

0

V

<

OUT

+2.5V

<

V

OUT

V

REF

V

DD

V

IN

OPA277

GND

I

1

OUT

R

FB

V

DD

V

OUT

I

2

OUT

C

1

DAC7822

Bipolar Output Section

V

D

0.5

*1

V

REF

(2)

DAC7822

SBAS374A – JUNE 2006 – REVISED JULY 2007

Table 2. Suitable High Speed Operational Amplifiers from Texas Instruments (Multiple Channel Options)

SUPPLY

GBW

VOLTAGE

GBW

SLEW

CMRR

VOLTAGE

PRODUCT

NOISE

(typ)

RATE

(typ)

(max)

(min)

PACKAGE/

PRODUCT

(V)

(MHz)

nV/

√Hz

(MHz)

(V/

μs)

(

μV)

(

μV)

(dB)

LEAD

DESCRIPTION

Single Channel

Very Low-Power High Speed

SOT5-23,

Rail-To-Rail Input/Output

THS4281

±2.7 to ±15

38

12.5

35

500

3500

500

1000

MSOP-8,

Voltage Feedback

SOIC-8

Operational Amplifier

CDIP-8,

100-MHz Low Noise

THS4031

±4.5 to ±16.5

200

1.6

100

500

3000

3000

8000

MSOP-8,

Voltage-Feedback Amplifier

SOIC-8

SOIC-8,

High Speed FET-Input

THS4631

±4.5 to ±16.5

210

7

900

260

2000

50pA

2

MSOP-8

Operational Amplifier

Wideband, Unity Gain Stable

SOIC-8,

OPA656

±4 to ±6

230

7

290

250

2600

2pA

5pA

FET-Input Operational

SOT5-23

Amplifier

Unity Gain Stable, Low

SOIC-8,

OPA820

±2.5 to ±6

280

2.5

240

200

1200

900

23,000

Noise, Voltage Feedback

SOT5-23

Operational Amplifier

Dual Channel

100-MHz Low Noise

SOIC-8,

THS4032

±4.5 to ±16.5

200

1.6

100

500

3000

3000

8000

Voltage-Feedback Amplifier,

MSOP-8

Dual

SpeedPlus Dual Wideband,

SOIC-8,

OPA2822

±2 to ±6.3

220

2

170

200

1200

9600

12000

Low-Noise Operational

MSOP-8

Amplifier

As Figure 40 illustrates, in order to generate a positive voltage output, a negative reference is input to the

DAC7822. This design is suggested instead of using an inverting amp to invert the output as a result of resistor

and a –2.5V input to the DAC7822 with an op amp.

Figure 40. Positive Voltage Output Circuit

The DAC7822, as a 2-quadrant multiplying DAC, can be used to generate a unipolar output. The polarity of the

Some applications require full 4-quadrant multiplying capabilities or bipolar output swing. As shown in Figure 41,

external op amp U2 is added as a summing amp and has a gain of 2X that widens the output span to 5V. A

4-quadrant multiplying circuit is implemented by using a 2.5V offset of the reference voltage to bias U2.

According to the circuit transfer equation given in Equation 2, input data (D) from code 0 to full-scale produce

15

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