A GFSK demodulator for low-IF Bluetooth receiver - Page 1
Forum section: electronics / projects

author: promach
author_rank: Frequent Contributor
timestamp: January 31, 2021, 01:59:14 pm
content: ForA GFSK demodulator for low-IF Bluetooth receiver, how does the shape-keeping circuit in figure 4(c) works ?Besides, why need the NOR gate before the input to the shape-keeping circuit ?

author: promach
author_rank: Frequent Contributor
timestamp: February 06, 2021, 08:14:52 am
content: I have thedraft circuitimplemented in LTSpice.Could anyone comment on it ?

author: R_G_B_
author_rank: Frequent Contributor
timestamp: February 11, 2021, 07:46:48 am
content: Shape keepingIt says the oneshot is used to reshape the output pulses.

author: promach
author_rank: Frequent Contributor
timestamp: February 11, 2021, 07:55:54 am
content: Why if R3 is changed to 50 ohm, thenthe whole circuitcannot simulate at all ?

author: R_G_B_
author_rank: Frequent Contributor
timestamp: February 11, 2021, 08:01:15 am
content: Pulses are combined hence the combinational logic or and nor.Do you have a copy of the spice files for ltspice?

author: promach
author_rank: Frequent Contributor
timestamp: February 11, 2021, 08:10:22 am
content: Just click "Download Zip" from the top right of thisgist link

author: promach
author_rank: Frequent Contributor
timestamp: February 12, 2021, 03:51:38 am
content: @R_G_B_What do you exactly mean byPulses are combined hence the combinational logic or and nor.?

author: R_G_B_
author_rank: Frequent Contributor
timestamp: February 12, 2021, 07:24:41 am
content: HiI have not down loaded the ltspice file so I'm not of the problem with your circuit.The or gates act like a full wave rectifier..frequency doubler. The pulse trains created from the I and Q inputs are combined through the nor logic. This combination of pulses is shaped so that all pulses are the same width. Then averaged to give a D.C value that represents the change in frequency.

author: promach
author_rank: Frequent Contributor
timestamp: February 12, 2021, 11:31:34 am
content: What is the purpose of the window comparator circuit consisting of U1, U2, R1, R2, R3 in the context of shape-keeping one-shot circuit ?Note that: Changing R3 from 100 ohm to 50 ohm will generate invalid output states for the SR latch (A12, A14), hence the pseudo transient analysis issue mentioned few days ago.

author: promach
author_rank: Frequent Contributor
timestamp: February 13, 2021, 10:02:23 am
content: See the attached zip file containing the spice file and the library.1. As for the stalled pseudo transient simulation analysis issue, just press `ESC` key for now to go directly to transient simulation.I had already added the `initial_reset_pulse` signal as well as .IC statements, but they still do not help.Do anyone know why ?2. As for the small V(out) difference for the demodulated signal, could anyone advise why ? I had narrowed down that the root cause is due to the bessel low-pass filter circuit to the right of A16

author: promach
author_rank: Frequent Contributor
timestamp: February 13, 2021, 01:32:54 pm
content: Now, I have 385mV for the V(out) output variation. See the attached zip file.But how to solve the pseudo transient analysis issue given that I already had .IC statements as well as 'initial_reset_pulse' signal ?

author: promach
author_rank: Frequent Contributor
timestamp: February 13, 2021, 06:20:06 pm
content: Seehttps://github.com/promach/GFSK