JAJSLI5J January 2011 – March 2021 OPA2835 , OPA835
PRODUCTION DATA
Figure 9-2 shows an amplifier circuit that converts single-ended signals to differential signals and provides gain and level shifting. This circuit can convert signals to differential in applications such as driving Cat5 cabling or driving differential-input SAR and ΔΣ ADCs.
By setting VIN = VREF + VSIG, then the output of the amplifier may be calculated according to Equation 4.
The differential-signal gain of the circuit is 2 × G, and VREF provides a reference around which the output signal swings. The differential output signal is in-phase with the single-ended input signal.
Line termination on the output can be accomplished with resistors RO. The differential impedance seen from the line will be 2 × RO. For example, if 100-Ω Cat5 cable is used with double termination, the amplifier is typically set for a differential gain of 2 V/V (6 dB) with RF = 0 Ω (short) RG = ∞Ω (open), 2R = 2 kΩ, R1 = 0 Ω, R = 1 kΩ to balance the input bias currents, and RO = 49.9 Ω for output line termination. This configuration is shown in Figure 9-3.
For driving a differential-input ADC the situation is similar, but the output resistors, RO, are selected with a capacitor across the ADC input for optimum filtering and settling-time performance.