THS770012_15 Datasheet, PDF (16/35 Pages) Texas Instruments – Broadband, Fully-Differential, 14-/16-Bit ADC Driver Amplifier

THS770012
SLOS669C – FEBRUARY 2010 – REVISED JANUARY 2012
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TEST DESCRIPTIONS
The following sections describe how the tests were performed, as well as the EVM circuit modifications that were
made (if any). Modifications made for test purposes include changing capacitors to resistors, resistors to
capacitors, the shorting/opening of components, etc., as noted. Unless otherwise noted, C1, C2, C9, and C13
are all changed to 0.1µF to give basically flat frequency response from below 1MHz to the bandwidth of the
amplifier, and gain is set to nominal +12dB.
Frequency Response: 200mV_PP, 2V_PP, 3V_pp
The test is run on the standard EVM using the transformers in the signal path.
A network analyzer is connected to the input and output of the EVM with 50Ω coaxial cables and set to measure
the forward transfer function (s21). The input signal frequency is swept with signal level set for desired output
amplitude.
The test ran for gains of +10dB, +11dB, +12dB and +13.7dB with component values changed per Table 2 in
Setting the Gain section.
s-Parameters: s11, s22, and s12
The standard EVM is used with both R15 and R17 = 24.9Ω, and R16 = open, to test the input return loss, output
return loss, and reverse isolation. A network analyzer is connected to the input and output of the EVM with 50Ω
coaxial cables and set to measure the appropriate transfer function: s11, s22, or s12. Note the transformers are
included in the signal chain in order to retrieve proper measurements with single-ended test equipment. The
impact is minimal from 10MHz to 200MHz, but further analysis is required to fully de-embed the respective
effects.
Frequency Response with Capacitive Load
The standard EVM is used with R15 and R17 = R_O, R16 = C_LOAD, C9 and C13 = 953Ω, R21 = open, T2
removed, and jumpers placed across terminals 3 to 4 and 1 to 6. A network analyzer is connected to the input
and output of the EVM with 50Ω coaxial cables and set to measure the forward transfer function (s21). Different
values of load capacitance are placed on the output (at R16) and the output resistor values (R15 and R17)
changed until an optimally flat frequency response is achieved with maximum bandwidth.
Distortion
The standard EVM is used for measurement of single-tone harmonic distortion and two-tone intermodulation
distortion. For differential distortion measurements, the standard EVM is used with no modification. For
single-ended input distortion measurements, the standard EVM is used with with T1 removed and jumpers
placed across terminals 3 to 4 and 1 to 6, and R5 and R6 = 100Ω. A signal generator is connected to the J1
input of the EVM with 50Ω coaxial cables, with filters inserted inline to reduce distortion from the generator. The
J3 output of the EVM is connected with 50Ω coaxial cables to a spectrum analyzer to measure the
fundamental(s) and distortion products.
Noise Figure
The standard EVM is used with T1 changed to a 1:2 impedance ratio transformer (Mini-Circuits ADT2), R15 and
R17 = 24.9Ω, and R5, R6, and R16 = open. A noise figure analyzer is connected to the input and output of the
EVM with 50Ω coaxial cables. The noise figure analyzer provides a 50Ω (noise) source so that the data are
adjusted to refer to a 100Ω source.
Transient Response, Slew Rate, Overdrive Recovery
The standard EVM is used with T1 and T2 removed and jumpers placed across terminals 3 to 4 and 1 to 6; R15,
R17, and R25 = 49.9Ω; C1, C2, C9, and C13 = 0Ω; and R5, R6, R16, and R21 = open. A differential waveform
generator is connected to the input of the EVM with 50Ω coaxial cables at J1 and J2. The differential output at J3
and J4 is connected with 50Ω coaxial cables to an oscilloscope to measure the outputs. Waveform math in the
oscilloscope is used to combine the differential output of the device.
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