ADA4806-1ARJZ-R7 datasheet(21/25 Pages) AD

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ADA4806-1

Data Sheet

APPLICATIONS INFORMATION

SLEW ENHANCEMENT

The ADA4806-1 has an internal slew enhancement circuit that

increases the slew rate as the feedback error voltage increases.

This circuit allows the amplifier to settle a large step response

faster, as shown in Figure 57. This is useful in ADC applications

where multiple input signals are multiplexed. The impact of the

slew enhancement can also be seen in the large signal frequency

response, where larger input signals cause a slight increase in

peaking, as shown in Figure 58.

TIME (ns)

100

VOUT = 500mV p-p

–0.5

–1.0

–1.5

0.5

1.0

1.5

VOUT = 2V p-p

VOUT = 1V p-p

VS = ±2.5V

G = +1

RL = 2kΩ

Figure 57. Step Response with Selected Output Steps

–6

–5

–4

–3

–2

–1

FREQUENCY (Hz)

VS = ±2.5V

G = +1

RL = 2kΩ

VIN = 400mV p-p

VIN = 100mV p-p

VIN = 200mV p-p

100k

10M

100M

VIN = 632mV p-p

VIN = 2V p-p

Figure 58. Peaking in Frequency Responses as Signal Level Changes, G = +1

EFFECT OF FEEDBACK RESISTOR ON FREQUENCY

RESPONSE

The amplifier input capacitance and feedback resistor form a

pole that, for larger value feedback resistors, can reduce phase

margin and contribute to peaking in the frequency response.

Figure 59 shows the peaking for selected feedback resistors (RF)

when the amplifier is configured in a gain of +2. Figure 59 also

shows how peaking can be mitigated with the addition of a

small value capacitor placed across the feedback resistor of the

amplifier.

–6

–5

–4

–3

–2

–1

FREQUENCY (Hz)

100k

10M

100M

RF = 1kΩ

RF = 2.6kΩ

RF = 2.6kΩ, CF = 1pF

RF = 4.99kΩ

RF = 4.99kΩ, CF = 1pF

VS = ±2.5V

G = +2

RL = 2 kΩ

VIN = 20mV p-p

Figure 59. Peaking in Frequency Response at Selected RF Values

COMPENSATING PEAKING IN LARGE SIGNAL

FREQUENCY RESPONSE

At high frequency, the slew enhancement circuit can contribute to

peaking in the large signal frequency response. Figure 59 shows the

effect of a feedback capacitor on the small signal response, whereas

Figure 60 shows that the same technique is effective for reducing

peaking in the large signal response.

–15

–12

–9

–6

–3

FREQUENCY (Hz)

VS = ±2.5V

G = +2

RL = 2 kΩ

VIN = 632mV p-p

RF = 2.6kΩ, CF = 0pF

RF = 1kΩ, CF = 0pF

RF = 2.6kΩ, CF = 2.7pF

RF = 1 kΩ, CF = 2 pF

100k

10M

100M

Figure 60. Peaking Mitigation in Large Signal Frequency Response

DRIVING LOW POWER, HIGH RESOLUTION

SUCCESSIVE APPROXIMATION REGISTER (SAR)

ADCs

The ADA4806-1 is ideal for driving low power, high resolution

SAR ADCs. The 5.9 nV/√Hz input voltage noise and rail-to-rail

output stage of the ADA4806-1 help minimize distortion at

large output levels. With its low power of 500 µA, the amplifier

consumes power that is compatible with low power SAR ADCs,

which are usually in the microwatt (µW) to low milliwatt (mW)

range. Furthermore, the ADA4806-1 supports a single-supply

configuration; the input common-mode range extends to 0.1 V

below the negative supply, and 1 V below the positive supply.

Rev. 0 | Page 20 of 24

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