Datasheet

=
1
2 R Cp
F F
GBP
4 R Cp
F D
(1)
GBP
2 R Cp
F D
f =
-3dB
(2)
OPA659
SBOS342B – DECEMBER 2008 – REVISED AUGUST 2009 ............................................................................................................................................ www.ti.com
To achieve a maximally flat second-order Butterworth turn requires a total feedback capacitance of 0.46pF.
frequency response, the feedback pole should be set Typical surface mount resistors have a parasitic
to: capacitance of 0.2pF, leaving the required 0.26pF
value to achieve the required feedback pole. This
calculation gives an approximate 4.9MHz, – 3dB
bandwidth computed by:
For example, adding the common mode and
differential mode input capacitance (0.7 + 2.8 =
3.5)pF to the diode source with the 20pF
capacitance, and targeting a 100k Ω transimpedance Table 3 lists the calculated component values and
gain using the 350MHz GBP for the OPA659, – 3dB bandwidths for various TIA gains and diode
requires a feedback pole set to 3.44MHz. This pole in capacitance.
Table 3. OPA659 TIA Component Values and Bandwidth for Various Diode Capacitance and Gains
C
DIODE
= 10pF
C
D
R
F
C
F
f
– 3dB
13.5 pF 1k Ω 3.50pF 64.24MHz
13.5 pF 10k Ω 1.11pF 20.31MHz
13.5 pF 100k Ω 0.35pF 6.42MHz
13.5 pF 1M Ω 0.11pF 2.03MHz
C
DIODE
= 20pF
23.5 pF 1k Ω 4.62pF 48.69MHz
23.5 pF 10k Ω 1.46pF 15.40MHz
23.5 pF 100k Ω 0.46pF 4.87MHz
23.5 pF 1M Ω 0.15pF 1.54MHz
C
DIODE
= 50pF
53.5 pF 1k Ω 6.98pF 32.27MHz
53.5 pF 10k Ω 2.21pF 10.20MHz
53.5 pF 100k Ω 0.70pF 3.23MHz
53.5 pF 1M Ω 0.22pF 1.02MHz
C
DIODE
= 100pF
103.5 pF 1k Ω 9.70pF 23.20MHz
103.5 pF 10k Ω 3.07pF 7.34MHz
103.5 pF 100k Ω 0.97pF 2.32MHz
103.5 pF 1M Ω 0.31pF 0.73MHz
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