THS4513-SP Datasheet, PDF (23/30 Pages) Texas Instruments – RAD-TOLERANT CLASS V, WIDEBAND, FULLY DIFFERENTIAL AMPLIFIER

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RS
V _Signal
RS
V _S+
R _PU
RG
RF
R_T
V _S+
V _S+
R _PU
R_G
RT
THS 4513
CM
V S-
R_O
V _OUT-
R_O
V _OUT+
R_F
Figure 64. THS4513 DC Coupled Single-Supply
With R_PU Used to Set V_IC
Figure 65 shows AC coupling to the source. Using
capacitors in series with the termination resistors
allows the amplifier to self-bias both input and output
to mid-supply.
R_S
C
R_G
R_F
V _Signal
R_S
R_T
C
R_G
R_T
V _S+= 3 V to 5 V
THS
CM
V _S-
R_O
V _OUT-
R_O
V _OUT+
C
C
R_F
Figure 65. THS4513 AC Coupled Single-Supply
THS4513-SP
SLOS539A – SEPTEMBER 2007 – REVISED OCTOBER 2007
impedance, termination, and 348 Ω feedback resistor.
Refer to Table 3 for component values to set proper
50 Ω termination for other common gains. A split
power supply of 4 V and –1 V is used to set the input
and output common-mode voltages to approximately
mid-supply while setting the input common-mode of
the ADS5500 to the recommended 1.55 V. This
maintains maximum headroom on the internal
transistors of the THS4513 to ensure optimum
performance.
From ^VIN
50 W
Source
49.9 W
0.22 mF
100 W
348 W
69.8 W
4V
0.22 mF
100 W
THS 4513
69..8 W
0.22 mF
CM
-1 V
348 W
100 W
100 W^{2.7 pF}
0.1 mF
14 Bit,
125 MSPS
A IN +
ADS5500
A IN - _CM
49.9 W
0.1 mF
Figure 66. THS4513 + ADS5500 Circuit
Figure 67 shows the 2-tone FFT of the THS4513 +
ADS5500 circuit with 65 MHz and 70 MHz input
frequencies. The SFDR is 90 dBc.
THS4513 + ADS5500 Combined Performance
The THS4513 is designed to be a high-performance
drive amplifier for high-performance data converters
like the ADS5500 14 bit 125 MSPS ADC. Figure 66
shows a circuit combining the two devices. The
THS4513 amplifier circuit provides 10 dB of gain,
converts the single-ended input to differential, and
sets the proper input common-mode voltage to the
ADS5500. The 100 Ω resistors and 2.7 pF capacitor
between the THS4513 outputs and ADS5500 inputs,
along with the input capacitance of the ADS5500,
limit the bandwidth of the signal to 115 MHz (–3 dB).
For testing, a signal generator is used for the signal
source. The generator is an AC-coupled 50 Ω source.
A band-pass filter is inserted in series with the input
to reduce harmonics and noise from the signal
source. Input termination is accomplished via the 69.8
Ω resistor and 0.22 μF capacitor to ground in
conjunction with the input impedance of the amplifier
circuit. A 0.22 μF capacitor and 49.9 Ω resistor is
inserted to ground across the 69.8 Ω resistor and
0.22 μF capacitor on the alternate input to balance
the circuit. Gain is a function of the source
Figure 67. THS4513 + ADS5500 2-Tone FFT With
65 MHz and 70 MHz Input
THS4513 + ADS5424 Combined Performance
Figure 68 shows the THS4513 driving the ADS5424
ADC.
The THS4513 amplifier provides 10 dB of gain,
converts the single-ended input to differential, and
sets the proper input common-mode voltage to the
ADS5424. Input termination and circuit testing is the
same as described above for the THS4513 +
ADS5500 circuit.
Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): THS4513-SP
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