Texas Instruments Single to Differential ADC Driver PCB for LMH6612 and LMH6619 (SOIC package, unstuffed) 551600074-001/ 551600074-001/NOPB 데이터 시트
제품 코드
551600074-001/NOPB
-27
-24
-21
-18
-15
-12
-9
-6
-3
0
3
N
O
R
MAL
IZ
ED
I
-V
G
AI
N
(
d
B
)
1M
10M
100M
FREQUENCY (Hz)
C
PD
= 330 pF,
C
F
= 22 pF
C
PD
= 222 pF,
C
F
= 18 pF
C
PD
= 100 pF,
C
F
= 12 pF
C
PD
= 22 pF,
C
F
= 5.6 pF
C
PD
= 47 pF,
C
F
= 8 pF
2
S
R
F
C
T
f
-3 dB
GBWP
=
C
F
=
C
T
2
S
R
F
(GBWP)
SNOSB00K – NOVEMBER 2007 – REVISED OCTOBER 2013
Theoretical expressions for calculating the optimum value of C
F
and the expected
−3 dB bandwidth are:
(7)
(8)
indicates that the
−3 dB bandwidth of the TIA is inversely proportional to the feedback resistor.
Therefore, if the bandwidth is important then the best approach would be to have a moderate transimpedance
gain stage followed by a broadband voltage gain stage.
gain stage followed by a broadband voltage gain stage.
shows the measurement results of the LMH6611 with different photodiodes having various capacitances
(C
PD
) and a feedback resistance (R
F
) of 1 k
Ω.
Table 4. TIA (
) Compensation and Performance Results
(1)
C
PD
C
T
C
F CAL
C
F USED
f
−3 dB CAL
f
−3 dB MEAS
Peaking
(pF)
(pF)
(pF)
(pF)
(MHz)
(MHz)
(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
(1)
GBWP = 130 MHz, C
T
= C
PD
+ C
IN
, C
IN
= 2 pF, V
S
= ±2.5V
shows the frequency response for the various photodiodes in
.
Figure 79. Frequency Response for Various Photodiode and Feedback Capacitors
When analyzing the noise at the output of the TIA, it is important to note that the various noise sources (that is,
op amp 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 output 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
op amp 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 output 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
). 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.
current and noise.
32
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