The LMH32404-Q1 is a highly integrated transimpedance amplifier device with four independent channels. Each channel has its own single-ended input, differential output stage and multiplexing switch. The integrated switch can be used to disconnect the differential output amplifier from the output pin, thereby enabling high-impedance output for the respective channel.

Figure 7-4 shows how this device feature can further save board space and cost by eliminating the need for discrete high-speed multiplexer in a system that consists of several amplifier channels multiplexed to a single ADC channel. When switching between different channels, the LMH32404-Q1 has a transition time of 10 ns (typical). The disabled channel outputs are high-impedance so multiple amplifier outputs can be directly shorted to each other. If one channel is enabled and other channels are disabled, the disabled channels will not load the enabled channel. This further makes the LMH32404-Q1 easy to use in photodiode array applications.

Set Mx (M1, M2, M3, or M4) high for the corresponding channel to be enabled and output switches closed. Set Mx to logic low (default state) for the corresponding channel to be disabled (standby mode) and output switches open. When the channel is in its standby power mode, the clamp circuitry is still active thereby protecting the TIA input. Also, when in standby mode, the ALC loop is still active depending on IDC_EN configuration.