AD812 datasheet(14/16 Pages) AD

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AD812

REV. B

–14–

1000

100

FREQUENCY – MHz

–3

–6

–9

VS = 15V

G = +2

RF = 750

RL = 1k

CL = 510pF, RS = 15

CL = 150pF, RS = 30

Figure 43. Response to Large Load Capacitor, VS = ±15 V

100

100ns

VIN

VOUT

Figure 44. Pulse Response of Circuit of Figure 41 with

CL = 510 pF, RL = 1 k

Ω, R

F = RG = 715

Ω, R

S = 15

Ω

Overload Recovery

There are three important overload conditions to consider.

They are due to input common mode voltage overdrive, input

current overdrive, and output voltage overdrive. When the

amplifier is configured for low closed-loop gains, and its input

common-mode voltage range is exceeded, the recovery time will

be very fast, typically under 10 ns. When configured for a higher

gain, and overloaded at the output, the recovery time will also

be short. For example, in a gain of +10, with 6 dB of input

overdrive, the recovery time of the AD812 is about 10 ns.

100

50ns

VIN

VOUT

Figure 45. 6 dB Overload Recovery; G = 10, RL = 500 Ω,

VS = ±5 V

In the case of high gains with very high levels of input overdrive,

a longer recovery time may occur. For example, if the input

common-mode voltage range is exceeded in a gain of +10, the

recovery time will be on the order of 100 ns. This is primarily

due to current overloading of the input stage.

As noted in the warning under “Maximum Power Dissipation,”

a high level of input overdrive in a high noninverting gain circuit

can result in a large current flow in the input stage. For differ-

ential input voltages of less than about 1.25 V, this will be inter-

nally limited to less than 20 mA (decreasing with supply voltage).

For input overdrives which result in higher differential input

voltages, power dissipation in the input stage must be consid-

ered. It is recommended that external diode clamps be used in

cases where the differential input voltage is expected to exceed

1.25 V.

High Performance Video Line Driver

At a gain of +2, the AD812 makes an excellent driver for a back-

terminated 75

Ω video line. Low differential gain and phase

errors and wide 0.1 dB bandwidth can be realized over a wide

range of power supply voltage. Outstanding gain and group

delay matching are also attainable over the full operating supply

voltage range.

AD812

VIN

VOUT

+VS

0.1 F

–VS

CABLE

Figure 46. Gain of +2 Video Line Driver (RF = RG from

Table I)

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