LMH6612MA Datasheet, PDF (29/32 Pages) Texas Instruments – Single Supply 345 MHz Rail-to-Rail Output Amplifiers

TABLE 4. TIA (Figure 1) Compensation and Performance Results
C_PD
(pF)
C_T
(pF)
C_{F CAL}
(pF)
C_{F USED}
(pF)
f _{−3 dB CAL}
(MHz)
f _{−3 dB MEAS}
(MHz)
Peaking
(dB)
22
24
5.42
5.6
29.3
27.1
0.5
47
49
7.75
8
20.5
21
0.5
100
102
11.15
12
14.2
15.2
0.5
222
224
20.39
18
9.6
10.7
0.5
330
332
20.2
22
7.9
9
0.8
Note:
GBWP = 130 MHz
C_T = C_PD + C_IN
C_IN = 2 pF
V_S = ±2.5V
Figure 14 shows the frequency response for the various pho-
todiodes in Table 4.
noise voltage, feedback resistor thermal noise, input noise
current, photodiode noise current) do not all operate over the
same frequency band. Therefore, when the noise at the out-
put is calculated, this should be taken into account. The op
amp noise voltage will be gained up in the region between the
noise gain’s zero and pole (f_Z and f_P in Figure 13). The higher
the values of R_F and C_T, the sooner the noise gain peaking
starts and therefore its contribution to the total output noise
will be larger. It is advantageous to minimize C_IN by proper
choice of op amp or by applying a reverse bias across the
diode but this will be at the expense of excess dark current
and noise.
EVALUATION BOARD
National Semiconductor provides the following evaluation
board as a guide for high frequency layout and as an aid in
device testing and characterization. Many of the datasheet
plots were measured with this board:
30033635
FIGURE 14. Frequency Response for Various Photodiode
and Feedback Capacitors
Device
LMH6611MK
Package
TSOT23
Board Part #
LMH730216
This evaluation board can be shipped when a device sample
request is placed with National Semiconductor.
When analyzing the noise at the output of the TIA, it is im-
portant to note that the various noise sources (i.e. op amp
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