Introduction The THS1041 from Texas Instruments (TI) is a 10-bit, 40-MSPS, CMOS high-speed analog-to-digital converter (ADC). It has many good features, including a single 3-V supply, low power, a flexible input configuration, a built-in programmable gain amplifier (PGA), and a built-in clamp function. Because of these features, especially the built-in clamp function, the THS1041 has been used in various applications for many years. The clamp function enables the device to generate and output a buffered dc voltage for flexible ADC applications—for example, to provide a common-mode voltage for the ADC or to allow dc restora- tion on an ac-coupled video signal at the ADC analog input. This function can be enabled or disabled. As shown in Figure 1, the THS1041 clamp function consists of an on-chip digital-to-analog converter (DAC), logic control, a clamp input, a buffer, and a clamp output. The clamp output can be a continuous or interrupted dc signal depending on whether its Clamp pin receives a dc or pulse signal from an external source. When this interrupted dc signal is applied to the ADC single-ended (SE) input circuit to provide common-mode voltage, the dc stability at the ADC analog input becomes a concern. Some users have questioned dc stability when the clamp function and SE input configura- tion are applied at the same time. This article presents some test data that explains how the dc voltage behaves in this kind of application condition and how to get the best ADC performance when the clamp function is on.