Texas Instruments THS4601 Evaluation Module THS4601EVM THS4601EVM Datenbogen
Produktcode
THS4601EVM
Transimpedance Amplifier
3-5
EVM Applications
signal also places requirements on the amplifier’s dynamic range. Knowledge
of the source’s output current levels, coupled with a desired voltage swing on
the output, dictates the value of the feedback resistor, R4. The transfer
function from input to output is V
of the source’s output current levels, coupled with a desired voltage swing on
the output, dictates the value of the feedback resistor, R4. The transfer
function from input to output is V
OUT
= I
IN
R
F
.
The large gain-bandwidth product of the THS4601 provides the capability for
achieving both high transimpedance gain and wide bandwidth simultaneously.
In addition, the high power supply rails provide the potential for a very wide
dynamic range at the output, allowing for the use of input sources which
possess wide dynamic range. The combination of these characteristics makes
the THS4601 a design option for systems that require transimpedance
amplification of wideband, low-level input signals. A standard transimpedance
circuit is shown in Figure 3-5.
achieving both high transimpedance gain and wide bandwidth simultaneously.
In addition, the high power supply rails provide the potential for a very wide
dynamic range at the output, allowing for the use of input sources which
possess wide dynamic range. The combination of these characteristics makes
the THS4601 a design option for systems that require transimpedance
amplification of wideband, low-level input signals. A standard transimpedance
circuit is shown in Figure 3-5.
Figure 3-5. Wideband Photodiode Transimpedance Amplifier
U1
7
VS+
-Vbias
J1
Vin-
PHOTODIODE
Z1 0
R3 0
Z5
R4
Z4 0
2
3
4
6
THS4601
VS+
VS-
TP3
Vout
-
+
R5
0
Z3 0
J3
Vout
As indicated, the current source typically sets the requirements for gain,
speed, and dynamic range of the amplifier. For a given amplifier and source
combination, achievable performance is dictated by the following parameters:
the amplifier’s gain-bandwidth product, the amplifier’s input capacitance, the
source capacitance, the transimpedance gain, the amplifier’s slew rate, and
the amplifier’s output swing. From this information, the optimal performance
of a transimpedance circuit using a given amplifier can be determined. Optimal
is defined here as providing the required transimpedance gain with a
maximally flat frequency response.
speed, and dynamic range of the amplifier. For a given amplifier and source
combination, achievable performance is dictated by the following parameters:
the amplifier’s gain-bandwidth product, the amplifier’s input capacitance, the
source capacitance, the transimpedance gain, the amplifier’s slew rate, and
the amplifier’s output swing. From this information, the optimal performance
of a transimpedance circuit using a given amplifier can be determined. Optimal
is defined here as providing the required transimpedance gain with a
maximally flat frequency response.
For the circuit shown in Figure 3-5, all but one of the design parameters are
known; the feedback capacitor must be determined. Proper selection of the
feedback capacitor prevents an unstable design, controls pulse response
characteristics, provides maximally flat transimpedance bandwidth, and limits
broadband integrated noise. The maximally flat frequency response results in
Z5 calculated as shown below, where Z5 is the feedback capacitor, R4 is the
feedback resistor, C
known; the feedback capacitor must be determined. Proper selection of the
feedback capacitor prevents an unstable design, controls pulse response
characteristics, provides maximally flat transimpedance bandwidth, and limits
broadband integrated noise. The maximally flat frequency response results in
Z5 calculated as shown below, where Z5 is the feedback capacitor, R4 is the
feedback resistor, C
S
is the total source capacitance (including amplifier input
capacitance and parasitic capacitance at the inverting node), and GBP is the
gain-bandwidth product of the amplifier in Hertz.
gain-bandwidth product of the amplifier in Hertz.