AD8307

Data Sheet

Rev. F | Page 16 of 24

It can be desirable to increase the speed of the output response,

with the penalty of increased ripple. One way to do this is by

connecting a shunt load resistor from the OUT pin to ground,

which raises the low-pass corner frequency. This also alters the

logarithmic slope, for example, to 7.5 mV/dB using a 5.36 kΩ

resistor, while reducing the 10% to 90% rise time to 25 ns. The

ripple amplitude for the 50 MHz input remains at 0.5 mV, but

this is now equivalent to ±0.07 dB. If a negative supply is available,

the output pin can be connected directly to the summing node

of an external op amp connected as an inverting mode transresis-

tance stage.

Note that while the AD8307 can operate down to supply voltages

of 2.7 V, the output voltage limit is reduced when the supply

drops below 4 V. This characteristic is the result of necessary

headroom requirements, approximately two VBE drops, in the

design of the output stage.

1.25kΩ

25mV/dB

OUT

2µA/dB

0µA TO 220µA

INT

FROM ALL

DETECTORS

CFLT

C2

1pF

VPS

BIAS

1.25kΩ

1.25kΩ

~400mV

8.25kΩ

60kΩ

60µA

COM

R1

12.5kΩ

C1

2.5pF

3pF

LGP

LGM

1.25kΩ

4

7

5

2

Figure 31. Simplified Output Interface