Each differential output pair of the LMH32404 can directly drive a high-speed differential input ADC. Figure 8-1 shows how the effective signal the effective signal gain between the TIA input and the ADC input is 20 kΩ when driving an ADC with a 100-Ω differential input impedance (R_{ADC_IN} = 50 Ω). Equation 2 gives the effective signal gain between the TIA input and the ADC input when driving an ADC with any other value of differential input impedance (R_{ADC_IN} ≠ 50 Ω).

Equation 2.

where

• A_V = Differential gain from the TIA input to the ADC input
• R_{ADC_IN} = Input resistance of the ADC

Figure 8-2 shows that in some designs a matching resistor network can be inserted between the LMH32404 output and the ADC inputs. Equation 3 gives the effective gain from the TIA input to the ADC input when using a matching resistor network.

Equation 3.

where

• A_V = Gain from the TIA input to the ADC input
• R_{ADC_IN} = Differential input resistance of the ADC
• R_ISO = Series resistance between the TIA and ADC

Equation 4 gives the voltage to be applied at the VOD pin (pin 10) if a certain differential offset voltage (V_OD) is needed at the ADC input for the circuit in Figure 8-2.

Equation 4.

where

• VOD = Voltage applied at pin 10
• V_OD = Desired differential offset voltage at the ADC input
• R_{ADC_IN} = Differential input resistance of the ADC
• R_ISO = Series resistance between the TIA and ADC