This circuit doesn't make a lot of sense.
I think the intent was for Q1 to invert the output signal of the IR receiver. The IR receiver has a open drain (or open collector) output. It actively drives the line low when the appropriate IR signal is detected, and leaves it high impedance when not.
When the line is driven low, it looks like that was supposed to draw current from the base, which would cause the transistor to source current out its collector, which would raise the CLK input of U1. However, the transistor has it's emitter and collector flipped. Most BJTs still work with E-C flipped, although at lower gain. In this case, the gain needed is actually less than 1, so this circuit probably works as intended, although probably by accident.
Since dedicated logic chips are used, the inversion between the TSOP output and the CLK input was apparently required. A more normal circuit would use a microcontroller, which should be configurable to either input polarity. In that case only a single pullup resistor would be required.
This circuit is a mess for a number of reasons:
- The absolute maximum power voltage for these TSOP detectors is 6 V. That is also the maximum for the output pin. Powering one of these from 9 V is totally irresponsible, and really bad design. Some units may work, for a while, some of the time.
- C1 is in the wrong place. These TSOP sensors are notorious for requiring good power supply decoupling. A small 1 µF ceramic cap between the power and ground pins of the TSOP would have been appropriate. Connecting the cap to the output pin makes little sense. There is no need to filter the output if it is otherwise handled correctly. Perhaps C1 was added in response to observed glitches. However, those are likely due to the missing power supply decoupling in the first place.
- The relative values of R1 and R2 don't make sense. The transistor would, if used properly, supply some gain. It makes no sense for the base current to be 10x higher than the collector current.
- There is nothing making sure the transistor is really off when OUT goes to high impedance. Something like 100 kΩ between base and emitter (if emitter and collector were connected properly) would achieve that.
- The larger circuit (beyond the snippet I copied into this answer) uses another transistor. However, that transistor is also designated Q1. Duh!
Clearly this circuit was designed by someone that didn't know what they were doing, and who apparently didn't even read the TSOP datasheet. Move along. There is nothing to see here.