Quadrature Clock Generator Introduction

General

This stage divides the local oscillator output by 4 and shifts the phase of the dividend signals such that they are now one-fourth the LO frequency and 90 degrees separated in phase (i.e., in quadrature). Both signals are identical in all regards except phase. They will be used to clock the switch used in the Quadrature Sampling Detector (QSD) stage.

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Quadrature Clock Generator Schematic

(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)

Quadrature Clock Generatorschematic

(above schematic has clickable areas that can be used for navigation)

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Quadrature Clock Generator Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

CheckDesignationComponentMarkingCategoryOrientationNotesCircuit
U0574AC74 Dual D FF74AC74 74AC74SOIC-14Markings vary - look for "AC74"Quadrature Clock Generator
C360.1 uF(smt) black stripe (smt) black stripeSMT 1206  Quadrature Clock Generator
R0910 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6W  Quadrature Clock Generator
R1010 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6W  Quadrature Clock Generator

Quadrature Clock Generator Summary Build Notes

Quadrature Clock Generator Detailed Build Notes

Bottom of the Board

Quadrature Clock Generator Bottom View

Install SMT Components

CheckDesignationComponentMarkingCategoryOrientationNotes
U0574AC74 Dual D FF74AC74 74AC74SOIC-14
Take ESD precautions
Markings vary - look for "AC74"
C360.1 uF(smt) black stripe (smt) black stripeSMT 1206 

Top of the Board

Quadrature Clock Generator Top View

Install Voltage Divider

CheckDesignationComponentMarkingCategoryOrientationNotes
R0910 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6W 
R1010 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6W 

Quadrature Clock Generator Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Quadrature Clock Generator Testing

Test Voltage Divider

Test Setup

Apply USB and 12V power to the board

Connect the black lead of your ohmmeter to the "/QSD EN" wire at the bottom edge of the topside of the board

Probe the +5 and 2.5 V test points shown in the graphic. R9 and R10 provide a voltage divider that divides the 5V rail's voltage in half. Passing this test is essential to passing the next test and ensuring that the Quadrature Clock Generator works OK.

Test Voltage Divider

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
"+5" (red} at R9's hairpin leadV dc5_______
"2.5" (blue) at R10's hairpin leadV dc2.5_______

Test U5's Pin Voltages

Test Setup

It has been observed before that some digital meters are affected by the square wave signals on IC pins and do not always read correctly. The readings you get should approximate 2.5V . The best instrument may be a good oscilloscope. Just be prepared to see slightly different readings on pins 10-13 and 3-6, depending on your DMM (mine is not the best!)

Apply USB and 12V power to the board

Connect the black lead of your ohmmeter to the "/QSD EN" wire at the bottom edge of the topside of the board

From the bottom side of the board, probe pins 1-14 of U5 and note your measurements in the table below.

Test U5's Pin Voltages

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Pin 1V dc5_______
Pin 2V dc2.5_______
Pin 3V dc2.5_______
Pin 4V dc5_______
Pin 5V dc2.5_______
Pin 6V dc2.5_______
Pin 7V dc0_______
Pin 8V dc2.5_______
Pin 9V dc2.5_______
Pin 10V dc5_______
Pin 11V dc2.5_______
Pin 12V dc2.5_______
Pin 13V dc5_______
Pin 14V dc5_______

QSD Clock Signals

Test Setup

If you have a dual trace scope available, probe the two "QSD CLK (n)" test points and you should get a waveform similar to the one shown here.

Your mileage may vary, depending upon the desired center frequency you select and the quality of your scope (some scopes tend to have issues with these square waves - still, the scope should show two waveforms in quadrature at the desired center frequency).

Hint: Using the CFGR tool, select a frequency that your scope can handle. For example, the author's scope can handle a 3.5 MHz signal fairly well; that calls for a 16 MHz setting on the Local Oscillator which, divided by 4, yields the 3.5 MHz outputs of the Quadrature Clock Generator (QCG). The key here is to test that the QCG is functioning correctly

If you do not have a scope, you can use an HF RX tuned to an HF frequency, set the LO to output 4X that selected frequency, and connect a wire from the RX's antenna, and bring it close to another wire stuck in one of the "QSD CLK n" testpoints. You shoujld be able to hear the QCG's output and be pretty well-assured you have successfully completed this stage.

QSD Clock Signals
Local Oscillator Quadrature Sampling Detector