LMH6601-Q1 Datasheet, PDF (26/37 Pages) Texas Instruments – 250 MHz, 2.4V CMOS Operational Amplifier with Shutdown

LMH6601, LMH6601-Q1
SNOSAK9E – JUNE 2006 – REVISED MARCH 2013
www.ti.com
For any video line rate (HxV corresponding to the number of Active horizontal and vertical lines), the speed
requirements can be estimated if the Horizontal Active (KH%) and Vertical Active (KV%) numbers are known.
These percentages correspond to the percentages of the active number of lines (horizontal or vertical) to the total
number of lines as set by VESA standards. Here are the general expressions and the specific calculations for the
SVGA line rate shown in Table 2.
1
x KH x KV
REFRESH_RATE
PIXEL_TIME (ns) =
x 1 x 10⁵
HxV
1 _{x 76 x 96}
75 Hz
=
x 1 x 10⁵ = 20.3 ns
800 x 600
(6)
Requiring that an “On” pixel is illuminated to at least 90% of its final value before changing state will result in the
rise/fall time equal to, at most, ⅓ the pixel time as shown below:
PIXEL_TIME 20.3 ns
RISE/FALL_TIME =
3
= ₃ = 6.8 ns
(7)
Assuming a single pole frequency response roll-off characteristic for the closed loop amplifier used, we have:
0.35
0.35
-3 dB_BW = _{RISE/FALL_TIME} = _{6.8 ns} = 52 MHz
(8)
Rise/Fall times are 10%-90% transition times, which for a 2 V_PP video step would correspond to a total voltage
shift of 1.6V (80% of 2V). So, the Slew Rate requirement can be calculated as follows:
SR(V/Ps)
=
1.6V
RISE/FALL_TIME
(ns)
x
1
x
10³
=
1.6V
6.8 ns
=
237(V/Ps)
(9)
The LMH6601 specifications show that it would be a suitable choice for video amplifiers up to and including the
SVGA line rate as demonstrated above.
For more information about this topic and others relating to video amplifiers, see Application Note 1013
(SNVA031).
CURRENT TO VOLTAGE CONVERSION (TRANSIMPEDANCE AMPLIFIER (TIA))
Being capable of high speed and having ultra low input bias current makes the LMH6601 a natural choice for
Current to Voltage applications such as photodiode I-V conversion. In these type of applications, as shown in
Figure 59 below, the photodiode is tied to the inverting input of the amplifier with R_F set to the proper gain (gain
is measured in Ohms).
C_F
R_F
-
D₁
LMH6601
V_OUT
C_D
C_A
+ ^U1
V_BIAS
Figure 59. Typical Connection of a Photodiode Detector to an op amp
26
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LMH6601 LMH6601-Q1