Input / output impedance chip P4302 - Page 1
Forum section: electronics / projects

author: GGMM
author_rank: Frequent Contributor
timestamp: April 19, 2023, 05:57:55 pm
content: Hello,I’m working on a spectrum analyzer setup.This one has 2 inputs, one for low frequencies and one for high frequencies.Each input is made with a P4302 circuit, driven in series by an ESP32 for the choice of attenuation. (It is a kind of TinySA).The schematic is the same...and what I don’t understand, I have an input that is 50 ohms and the other 100 ohms. It’s the same on the output.I checked everything, resistance, capacitor, possible short circuit.I don’t know where that comes from, except for the chip. It is so tiny and difficult to weld even with hot air, that I would not change it immediately.an idea??I’m attaching a part of the input diagramcdtThe chip:https://www.alldatasheet.com/datasheet-pdf/pdf/231870/PEREGRINE/PE4302.html

author: GGMM
author_rank: Frequent Contributor
timestamp: April 20, 2023, 06:23:42 am
content: re,Desoldering and replacing, best solution?. P4302 may have suffered with hot air.I’ll measure the nine empty and then compare with the one unsoldered.It's best soulutioncdt

author: erikka
author_rank: Regular Contributor
timestamp: April 20, 2023, 06:41:40 am
content: What attenuation did you set the pe4302 to?If 0 dB the chip is feed through and you will measure the impedance at the output, infinite if left openIf 30dB you will measure 50 ohmsAnd depending on intermediate attenuation anything in between

author: GGMM
author_rank: Frequent Contributor
timestamp: April 20, 2023, 07:02:59 am
content: ErikkaThis is a power off measurement.The measurement is good on the high frequencies input as said, different on the low input which has the same electrical construction.Would the chip be so smart to retain the last programmed attenuation even when the power is off?So, what you mean is that we could have a different measure depending on the last attenuation choice and that it remains in memory in the chip.Why not? Is this noted in the datasheet? Tobe seecdt

author: erikka
author_rank: Regular Contributor
timestamp: April 20, 2023, 01:34:36 pm
content: When set to zero dBm, the default after power on, the input resistance of the componts connected to to output are measured and these are very different.You can only compere the two after removing the capacitor between the PE4302 and the rest of the circuit

author: GGMM
author_rank: Frequent Contributor
timestamp: April 20, 2023, 02:15:03 pm
content: Erikka,If I take that inputs J14 and J13. there is actually a capacitor, but connected to nothing because it goes to the SMA socket.So we can measure the circuit input, which is pin 14.This is where I don’t understand, for a P4302 I have 50 ohm (which seems right to me), for the other P4302 I 100 ohm.The basic question is:On a P4302 is the input impedance still at 50 ohm regardless of the attenuation choice? I think so, and it is inside the circuit that the attenuation is done. (Same, the output must always stay at 50 ohm the same way)I’ll take it off and see.For your information, I tested another P4302 chip . I have 40 ohms between pin 14 and the substrate (ground weight of the medium), but of course no other pin connected (ground or other)To seecdt

author: erikka
author_rank: Regular Contributor
timestamp: April 20, 2023, 06:12:44 pm
content: You are wrong about the internals. Look at the data sheet. It's a collection of PI attenuators can be bypassed. In 0 dB mode everything is bypassed and you literally see what is connected to the other side

author: GGMM
author_rank: Frequent Contributor
timestamp: April 21, 2023, 06:37:43 am
content: okThanks for the returnSo it would be best to disconnect the output capacitor and see if I have an output signal. it should therefore be variable with attenuation.I’ll see if this can be done with an arduino ESP32 programor directly with the spectral softwarecdt