LT1328 powering & photodiode multiplexing

Hi Pavel,

The LT1328's high-pass filter rejects low frequency noise, however the pin 1 bias voltage is still susceptible to drift from variations to the supply voltage.  Please refer to second TOC on page 3 of the datasheet (Change in Voltage on Pin 1 vs Supply Voltage).  High frequency noise on the supply can lead to jitter on the TTL signals.  If a low noise LDO is not used, I would recommend making sure that the supply pin bypass filter caps can handle any high frequency noise on the supply line.

Regarding multiplexing, I would recommend multiplexing the digital outputs rather than the analog inputs.

Regards,

Omar

Hi Pavel,

The LT1328's high-pass filter rejects low frequency noise, however the pin 1 bias voltage is still susceptible to drift from variations to the supply voltage.  Please refer to second TOC on page 3 of the datasheet (Change in Voltage on Pin 1 vs Supply Voltage).  High frequency noise on the supply can lead to jitter on the TTL signals.  If a low noise LDO is not used, I would recommend making sure that the supply pin bypass filter caps can handle any high frequency noise on the supply line.

Regarding multiplexing, I would recommend multiplexing the digital outputs rather than the analog inputs.

Regards,

Omar

Hi Omar,

Thanks. So you think it would be wise to use low-noise LDOs ... like these ones (LDLN025 from ST and LT3045 from Analog Device) ? What about one LDO per one LT1328 ... or one LDO for multiple LT1328 will be also Ok ?

ONojan said:

multiplexing the digital outputs rather than the analog inputs

Ok

Sincerely,

Pavel

Hi Pavel,

Adding LDO will help to improve the noise performance. Whether using one or eight LDOs in your new design depends on your noise requirements for your system and the noise level from your supply. One LDO can supply eight infrared receivers but might not be optimal for noise performance if their locations are far away from each other.

Best,

Jane

Hi Jane,

Thanks. Eight LT1328 (as well as theirs photodiodes) will be quite close each other on PCB. Perhaps using one LDO in star configuration (i.e. VCC of LT1328 goes directly to LDO output) for eight LT1328 using ferrite beds for isolation will be Ok ?

Hi Pavel, ferrite bead(s) can be added if the system is required, typically placed before an LDO. 

Hi Jane,

I thought place ferrite beads between LDO output and VCCs of eight LT1328.

Hi Pavel,

An LDO is sensitive with a ferrite bead. If you need support for LT3045, we can forward your question to Power Management forums. However, it doesn’t hurt to add footprints for ferrite bead(s) on your prototype board and verify whether you need it or not.