Quadrature Clock Generator Introduction


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)

(Click for Full Schematic)
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)

C48band-specificmisc  Quadrature Clock Generator
hf-jmpband-specificmisc  Quadrature Clock Generator
C360.1 uF(smt) black stripe (smt) black stripeSMT 1206yellow pads Quadrature Clock Generator
R1010 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6WS-N Quadrature Clock Generator
R1110 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6WN-S Quadrature Clock Generator
U0674AC74 Dual D FF74AC74 74AC74SOIC-14Markings vary - look for "AC74"Quadrature Clock Generator
U12band-specificmisc  Quadrature Clock Generator

Band Specific Items for HF Band

C48omit for this bandOmit  Quadrature Clock Generator
hf-jmpshunt wire (cut-off lead)Cutoff  Quadrature Clock Generator
U12omit for this bandOmit  Quadrature Clock Generator

Band Specific Items for LF Band

C480.1 uF(smt) black stripe (smt) black stripeSMT 1206  Quadrature Clock Generator
hf-jmpomit for this bandOmit  Quadrature Clock Generator
U1274AC74 Dual D FF74AC74 74AC74SOIC-14  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 ICs and SMT Capacitors

Here, you will install U6 (to get a divide-by-4) and, if building the LF option, U12 (to get a divide-by-16); also installed will be the appropriate SMT bypass capacitors.

U6 is required for both HF and LF options; U12 is only needed for the LF option. Watch out for the potential to install U6 in the wrong set of pads!

HFomit for this band (Omit)
LF0.1 uF (SMT 1206)(smt) black stripe
C360.1 uF(smt) black stripe (smt) black stripeSMT 1206yellow pads
U0674AC74 Dual D FF74AC74 74AC74SOIC-14
Take ESD precautions
Markings vary - look for "AC74"
HFomit for this band (Omit)
LF74AC74 Dual D FF (SOIC-14)74AC74

Top of the Board

Quadrature Clock Generator Top View

Install Voltage Divider Resistors

Pay careful attention to the orientation (S-N and N-S, respectively) of R10 and R11. Some builders have inadvertently installed these with a horizontal orientation rather than a vertical orientation.

R1010 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6WS-N
R1110 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6WN-S

Install HF Jumper

If building the HF option, omit U12 and Install the jumper wire to bypass U12 with the LO signal

Install HF Jumper photo
HFshunt wire (cut-off lead) (Cutoff)
LFomit for this band (Omit)

Quadrature Clock Generator Completed Stage

(These photos were of an earlier board design. It has changed since the author built the kit upon which these notes are based. The board layout graphics are, however, current.)

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Quadrature Clock Generator Testing

Current Draw

Test Setup

With both the USB cable and the power cable plugged in, measure the current draw in the positive power lead.

Measure the current draw with just the 12V power.

Note: the current draw will be slightly higher if you installed U12 as part of an LF option build

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Current draw WITH USBmA< 189.8_______
Current draw NO USBmA< 2013.7_______

Test Voltage Divider

Test Setup

When performing the following tests, you must apply [pwer to the board AND plug in the USB cable. Otherwise, results will not be as expected.

Plug in USB and power the board.

Measure the voltage on the R11 hairpin; you should see 50% of the %v rail voltage.

Depending upon your DMM, your measurements may vary. What we are looking for here is roughly half the 5 volt rail

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
R11 hairpin (WRT regular gnd)V dc2.52.46_______

Divider Pin Voltages

Test Setup

Power USB and 12V. Then measure the voltages on the pins (and, separately, on the pads) of U6 (74AC74). Refer to the color codes on the graphic for the voltages.

Pins 3 and 11 will not show exactly 2.5Vdc because they have the additional AC component of the local oscillator signal from C3. The important idea is - for those pins which should nominally be 2.5Vdc - you do NOT want to see 0 or 5 Vdc!

If you are building the LF option, you should perform this test on both U12 and U6; otherwise, just test U6.

Divider Pin Voltages

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Pin 1Vdc54.92_______
Pin 2Vdc2.52.45_______
Pin 3Vdc2 to 32.46_______
Pin 4Vdc54.92_______
Pin 5Vdc2.52.45_______
Pin 6Vdc2.52.45_______
Pin 7Vdc0 (GND)0_______
Pin 8Vdc2.52.45_______
Pin 9Vdc2.52.45_______
Pin 10Vdc54.92_______
Pin 11Vdc2.52.46_______
Pin 12Vdc2 - 32.45_______
Pin 13Vdc54.92_______
Pin 14Vdc54.92_______

Quadrature Colck Generated Waveforms

Test Setup

Set your board up to oscillate at a selected center frequency, e.g., 7.100 MHz.

clock test points

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.

The testpoint marked "LO Clock" will provide the Si570's output frequency or, in the case of the LF option, that frequency divided by 4 (courtesy of U12).

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).

Quadrature Colck Generated Waveforms
Local Oscillator's Output 2,5V test point Quadrature Clock Signals for Clocking the QSD ("mixer") From (Digital) Power Supply