THS770006 Datasheet, PDF (14/39 Pages) National Semiconductor (TI) – Broadband, Fully-Differential, 14-/16-Bit ADC DRIVER AMPLIFIER

THS770006
SBOS520B – JULY 2010 – REVISED JANUARY 2012
TEST CIRCUITS
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OVERVIEW
The standard THS770006 evaluation module (EVM) is used for testing the typical performance shown in the
Typical Characteristics, with changes as noted below. The EVM schematic is shown in Figure 33. The signal
generators and analyzers used for most tests have single-ended 50Ω input and output impedance. The
THS770006 EVM is configured to convert to and from a differential 50Ω impedance by using RF transformers or
baluns (CX2156NL from Pulse, supplied as a standard configuration of the EVM). For line input termination, two
49.9Ω resistors (R5 and R6) are placed to ground on the input transformer output pins (terminals 1 and 3). In
combination with the 100Ω input impedance of the device, the total impedance seen by the line is 50Ω.
A resistor network is used on the amplifier output to present various loads (R_L) and maintain line output
termination to 50Ω. Depending on the test conditions, component values are changed as shown in Table 1, or as
otherwise noted. As a result of the voltage divider on the output formed by the load component values, the
amplifier output is attenuated. The Loss column in Table 1 shows the attenuation expected from the resistor
divider. The output transformer causes slightly more loss, so these numbers are approximate.
Table 1. Load Component Values⁽¹⁾
LOAD R_L
100Ω
200Ω
400Ω
1kΩ
R15 AND R17
25Ω
86.6Ω
187Ω
487Ω
R16
Open
69.8Ω
57.6Ω
52.3Ω
LOSS
6dB
16.8dB
25.5dB
31.8dB
(1) The total load includes 50Ω termination by the test equipment. Components are chosen to achieve load and 50Ω line termination
through a 1:1 transformer.
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