Datasheet

ADS1194, ADS1196

ADS1198

SBAS471C –APRIL 2010– REVISED NOVEMBER 2011

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RIGHT LEG DRIVE (RLD DC BIAS CIRCUIT)

The right leg drive (RLD) circuitry is used as a means to counter the common-mode interference in a ECG

system as a result of power lines and other sources, including fluorescent lights. The RLD circuit senses the

common-mode of a selected set of electrodes and creates a negative feedback loop by driving the body with an

inverted common-mode signal. The negative feedback loop restricts the common-mode movement to a narrow

range, depending on the loop gain. Stabilizing the entire loop is specific to the individual user system based on

the various poles in the loop. The ADS1194/6/8 integrates the muxes to select the channel and an operational

amplifier. All the amplifier terminals are available at the pins, allowing the user to choose the components for the

feedback loop. The circuit in Figure 50 shows the overall functional connectivity for the RLD bias circuit.

The reference voltage for the right leg drive can be chosen to be internally generated (AVDD + AVSS)/2 or it can

be provided externally with a resistive divider. The selection of an internal versus external reference voltage for

the RLD loop is defined by writing the appropriate value to the RLDREF_INT bit in the COFIG3 register.

If the RLD function is not used, the amplifier can be powered down using the PD_RLD bit (see the CONFIG3:

Configuration Register 3 subsection of the Register Map section for details). This bit is also used in daisy-chain

mode to power-down all but one of the RLD amplifiers.

The functionality of the RLDIN pin is explained in the Input Multiplexer section. An example procedure to use the

RLD amplifier is shown in the Right Leg Drive subsection of the Quick-Start Guide section.

Product Folder Link(s): ADS1194 ADS1196 ADS1198