IR remote-control receiver design - getting it stable

The best (discrete) IR remote-control receiver I have ever used, a Hitachi design from an old JCTV-3100. Fantastic range over 50m and used in large halls, works with IR bouncing off many surfaces :thumbsup:

I duplicated the circuit on a PCB. Works but it is oscillating at around 58kHz, and does pick up AM radio. It has a fair bit of noise and is very sensitive- putting a grounded probe near Q2 can lessen the oscillations. Putting a finger inches anywhere near the front-end it picks up interference. A wire mesh covering the photo-diode stops the AM radio ingress. A metal shielded enclosure, like the original has helps but it is still baffling me with the 58kHz. The transformer is tuned to 38kHz.

Adding a 68pF cap across C-B on Q4 stabilizes (fixes) the circuit but also lowers sensitivity (at 38kHz). This is the best I could come up with.

Any ideas how to tame the bandwidth and stabilize the circuit? The PCB has a ground-pour on both sides and does not seem to be the problem, and power is clean, 9V battery gives same results.

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Hi,

Any ideas how to tame the bandwidth and stabilize the circuit? The PCB has a ground-pour on both sides and does not seem to be the problem

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I don't agree.
A copper pour in my eyes isn't much better than single wires. Every cut reduces the HF stability of the GND plane.

Thus I recommend to show us your PCB layout.

Klaus

The original Hitachi design was split into two (single-sided) boards. "Photo Amp" with metal can shielding Q1-Q3 and then a connector & shielded cable to the second board with Q4-Q7. I measure about 120pF capacitance on that cable, it would be from C8 to GND.

I put it all on one new PCB:
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Original Hitachi build:
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Hi,

Your pictures show many different designs.
I can't find out which one is your current design.

Klaus

Sorry, here are pictures of just what I built.

Assembled PCB
Bottom Layer PCB
Top Layer PCB

Hi,

I wonder why all your transistors are not in the same orientation than the silk screen shows.


Klaus