9042 Datasheet, PDF (18/26 Pages) Maxwell Technologies – 12-Bit, 41 MSPS A/D Converter

12-Bit, 41 MSPS A/D Converter
Figure 21. Raise Logic Threshold for Encode
9042
While the single-ended encode will work well for many applications, driving the encode differentially will provide
increased performance. Depending on circuit layout and system noise, a 1 dB to 3 dB improvement in SNR can be
realized. It is not recommended that differential TTL logic be used however, because most TTL families that support
complementary outputs are not delay or slew rate matched. Instead, it is recommended that the encode signal be ac-
coupled into the ENCODE and ENCODE pins.
The simplest option is shown below. The low jitter TTL signal is coupled with a limiting resistor, typically 100 ohms, to
the primary side of an RF transformer (these transformers are inexpensive and readily available; part# in Figure 22 is
from Mini-Circuits). The secondary side is connected to the ENCODE and ENCODE pins of the converter. Since both
encode inputs are self biased, no additional components are required.
Figure 22. TTL Source – Differential Encode
01.07.05 REV 7
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