OPA683ID datasheet(13/31 Pages) TI

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OPA683

SBOS221E

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into this midpoint voltage bias. The input voltage can swing

to within 1.25V of either supply pin, giving a 2.5VPP input

signal range centered between the supply pins. The input

impedance of Figure 3 is set to give a 50

Ω input match. If the

source does not require a 50

Ω match, remove this and drive

directly into the blocking capacitor. The source will then see

the 6.25k

Ω load of the biasing network. The gain resistor

(RG) is AC-coupled, giving the circuit a DC gain of +1—which

puts the noninverting input DC bias voltage (2.5V) on the

output as well. The feedback resistor value has been ad-

justed from the bipolar supply condition to re-optimize for a

flat frequency response in +5V only, gain of +2 operation. On

a single +5V supply, the output voltage can swing to within

1.0V of either supply pin while delivering more than 50mA

output current giving 3VPP output swing into an AC-coupled

100

Ω load if required (8dBm maximum at the matched load).

The circuit of Figure 3 shows a blocking capacitor driving into

a 1k

Ω load resistor. Alternatively, the blocking capacitor

could be removed if the load is tied to a supply midpoint or

to ground if the DC current required by the load is accept-

able.

Figure 4 shows the AC-coupled, single +5V supply, gain of

–1V/V circuit configuration used as a basis for the +5V only

Typical Characteristics. In this case, the midpoint DC bias on

the noninverting input is also decoupled with an additional

0.1

µF decoupling capacitor. This reduces the source imped-

ance at higher frequencies for the noninverting input bias

current noise. This 2.5V bias on the noninverting input pin

appears on the inverting input pin and, since RG is DC

blocked by the input capacitor, will also appear at the output

pin. One advantage to inverting operation is that since there

is no signal swing across the input stage, higher slew rates

and operation to even lower supply voltages is possible. To

retain a 1VPP output capability, operation down to a 3V

supply is allowed. At a +3V supply, the input stage is

saturated, but for the inverting configuration of a current-

feedback amplifier, wideband operation is retained even

under this condition.

The circuits of Figure 3 and 4 show single-supply operation

at +5V. These same circuits may be used up to single

supplies of +12V with minimal changes in the performance of

the OPA683.

LOW POWER, VIDEO LINE DRIVER

APPLICATIONS

For low power, video line driving, the OPA683 provides the

output current and linearity to support multiple load compos-

ite video signals. Figure 5 shows a typical

±5V supply video

line driver application. The improved 2nd-harmonic distortion

of the CFBplus architecture, along with the OPA683’s high

output current and voltage, gives exceptional differential gain

and phase performance in a very low power solution. As the

Typical Characteristics show, a single video load shows a

dG/dP of 0.06%/0.03

°. Multiple loads may also be driven with

< 0.15%/0.1

° dG/dP for up to 4 parallel video loads where the

amplifier is driving an equivalent load of 37.5

Ω.

1.4k

Ω

OPA683

+5V

DIS

Ω Source

0.1

µF

6.8

µF

12.5k

Ω

2.5V

12.5k

Ω

1.4k

Ω

0.1

µF

0.1

µF

0.1

µF

Ω

FIGURE 3. AC-Coupled, G = +2V/V, Single-Supply, Specifi-

cation and Test Circuit.

1.4k

Ω

OPA683

+5V

DIS

Ω Source

0.1

µF

0.1

µF

2.5V

6.8

µF

1.4k

Ω

12.5k

Ω

12.5k

Ω

0.1

µF

52.3

Ω

0.1

µF

Ω

FIGURE 4. AC-Coupled, G = –1V/V, Single-Supply, Specifi-

cation and Test Circuit.

1.2k

Ω

OPA683

+5V

DIS

–5V

Ω

1.2k

Ω

Ω Load

Supply Decoupling not shown.

Coax

VIDEO

FIGURE 5. Gain of +2 Video Cable Driver.

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