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AN-557 APPLICATION NOTE

One Technology Way · P.O. Box 9106 · Norwood, MA 02062-9106 · 781 / 329-4700 · World Wide Web Site: http://www.analog.com

AN-557 APPLICATION NOTE
One Technology Way · P.O. Box 9106 · Norwood, MA 02062-9106 · 781 / 329-4700 · World Wide Web Site: http://www.analog.com
PIC "N" MIX DIGITAL INJECTION SYSTEM
By Peter Rhodes, BSc, G3XJP (email pirrhodes@aol.com) PART 1 OF 5
This five-part article is reprinted in its entirety by permission of RadCom Magazine, a ham radio magazine publication in the U.K.(website www.rsgb.com), and the author. All international copyrights are reserved.
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CLKIN
REFERENCE CLOCK
AD9850
32-BIT TIMING WORD (GENERATED BY PIC)
Figure 1. DDS Block Diagram
The basic block diagram is shown in Figure 1. There is a simple relationship between the output frequency FOUT, the reference clock frequency CLKIN, and the 32bit tuning word Phase:
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(second image), 230 MHz (third image), 270 MHz (fourth image) . . . and so on.
AD9850 14-PIN DIL
AMPLITUDE
FIRST IMAGE 20
SECOND THIRD IMAGE IMAGE
FOURTH FIFTH IMAGE IMAGE 355
105 145 230 270 REFERENCE CLOCK CLKIN FREQUENCY - 125MHz
Figure 2. DDS Output Spectrum
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DDS BOARD DISPLAY BOARD
5V 12V
3-TO-8 DECODER
5V, 8V REGULATORS
5V TO LOGIC
8V TO REFERENCE OSCILLATOR
C BUFFER ENABLE 6 7
COMMON ANODE
PIC16C84
RA3 DIRECTION RB7 PULSES OSC1 4MHz OSC2 RB0 RB1 RB2 RB3
BCD TO A 7-SEG DECODER B C D E F G
RA0 5V RA1 RA2 110MHz REFERENCE CLOCK OSCILLATOR RB4 PTT LINE RB5 RB6
AD9850
8-BIT SR AND LATCH DATA CLOCK DISPLAY BOARD LATCH
USE USB IF USE CW IF USE LSB IF BROADBAND SPARE 1.8MHz 3.5MHz 7.0MHz
8-BIT SR AND LATCH DATA CLOCK LATCH
10MHz 14MHz 15MHz 18MHz 21MHz 24MHz 28MHz 29MHz
SWITCH OUTPUTS TO HOST Tx / Rx
8-BIT SR AND LATCH DATA CLOCK LATCH
Split
Figure 4. PIC "N" MIX block diagram, illustrating PIC input / output allocations and physical partitioning. Besides power supply distribution and decoupling, all functional elements are shown.
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In this issue the alternatives and techniques for mechanical construction are explored. These include a process for making one-off PCBs-and for mounting the DDS chip on a DIL socket carrier. OVERALL STRATEGY When it comes to the gross layout of the hardware, flexibility is a design objective. When it comes to the mounting of the DDS chip itself, a successful outcome is likely only if you absolutely follow the rules and allow me to adopt a somewhat dictatorial style. Your first decision revolves around whether you are building an external injection source or are integrating it mechanically with your Tx / Rx. In either case, self-evidently, the tuning knob and keypad need to go on the front panel with the display board immediately behind it. The DDS board is the same size as the display board. It is designed for mounting parallel to and behind the display board, or at right-angles to it, or completely remotely from it and connected to it by ribbon cable. The last choice is not relevant in a self-contained external source. The tuning knob may be mounted on either side of the display, the choice being governed simply by whether you are right or left-handed. The keypad should be mounted on the same side of the display as the tuning knob. Should you mount it on the opposite side of the display, although it may give some appearance of better aesthetic balance, you are courting an ergonomic disaster. Visual feedback of your key presses is given via the display and status LEDs and your forearm will inevitably obscure the view. In the photographs, you will note that my keypad is mounted contrary to these recommendations. This is a layout peculiar to my requirements since I am unusual in being mostly ambidextrous, preferring twisting
3.25" NOMINAL HEIGHT FRONT PANEL
DISPLAY BOARD - 6.1"
0.75" DISPLAY CUT-OUT
SIG GEN
Figure 5. Drilling template for front panel. The position of the tuning knob shown assumes you are mounting the shaft encoder on the display and DDS boards. It could be much further to the right or on the opposite side of the display.
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holes for equal protrusion. They are then tacked and finally soldered to the display board when fully aligned. If like me, you deprecate the idea of screw-heads showing on the front panel, then you will need to glue some nuts or threaded pillars to the back of the front panel to mount the display board. I find nut rivets ideal for this since they have a large surface area which makes for strong and permanent adhesion using super glue. DDS BOARD MOUNTING Figure 6 shows the configuration for right angle mounting and Figure 7 illustrates parallel mounting. To ensure full access during commissioning I would strongly recommend that you avoid the parallel mounting configuration to start with. If this is your target configuration, join the two boards with a short length of 0.1" pitch ribbon cable. This allows access to both sides of both boards for testing. If you are mounting the two boards at right angles in close proximity, then the best approach is to permanently solder the two boards together as shown in Figure 6. Butt the two boards to form a small "T" junction (not an "L"), tack them lightly together, check the angle and then run beads of solder along the full length of both
DISPLAY BOARD ACETATE DISC DISC MOUNTING KNOB FLYWHEEL FRONT BEARING
REAR BEARING
IR DETECTOR
IR DIODE
TUNING KNOB DDS BOARD
DISPLAY BOARD
FLYWHEEL
BEARINGS
IR DIODE
IR DETECTOR DDS BOARD
TUNING KNOB
Figure 7. Alternative mounting method (not-to-scale) where the DDS board is mounted parallel to the display board on spacers (not shown). A small hole is drilled in the DDS board to pass the infrared, and the rear bearings are fitted to the DDS board. The leads for the detector pass through the board to the tracks-which are cut to avoid interference with the rear bearing. The detail will become apparent when the DDS PCB is described later.
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Now focus on infinity and walk around for several minutes before addressing the other side. 15 16 17 18 19 20 21 22 23 24 25 26 27 28 leave leave leave up down leave leave down up down leave down down down
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8 COPPER FOIL POWER PLANE 5V 11 14
COPPER FOIL POWER PLANE 5V
22 21 20 19 PCB GROUND PLANE 15 18 17 16 REFOUT
Figure 8. DDS assembly. The DDS chip is mounted upside down (dead-bug) on the PCB ground plane. A strip of copper foil provides a low impedance power plane. Not shown is a 1n decoupling capacitor connected between the ground and power planes adjacent to Pin 1 on the chip.
Repeat this process for Pins 19, 26-28, 10, 22, 5, and 24 in that order. Make very sure you are operating on the correct legs. You can bend them up and down perhaps once before risking amputation but it is not worth the risk. Obtain a small strip of copper foil. Copper or brass shim stock would suffice. In the worst case, a suitable strip can be removed from a piece of scrap PCB with a sharp knife or stripped from some foil braided coax. It needs to be long enough to solder to Pins 7 and 8 of the socket, pass over the chip and down the other side to solder to Pins 21 and 22. The width needs to be the same as (or if anything, a whisker more than) the chip moulding width. It can be trimmed to size and trial fitted for width with a pair of scissors. Excess length can be removed later. Fix the foil to the chip moulding using a trace of super glue. When set, bend the ends down, trim to length and solder to the +5 V pins on the DIL socket (7 and 8, 21 and 22), making sure that it does not touch the PCB ground plane. Bend up completely all the +5 V pins on the chip, namely 3, 4, 6, 11, 18, 23 and then quickly solder each one to the foil. There now remains only to attach seven signal pins and to ease the process, some pins are bent down a little to near horizontal and some up a few degrees. This gives more clearance to get the soldering iron in. Bend Pins 8, 21, 25 up a little and Pins 7, 9, 12, 20 down a little. Trim the three resistors to size and solder down their earthy ends with the pin end just touching the end of the target pin, bending the resistors leads as necessary to get a touch on the end of the pins. Quickly solder the resistors to the pins. Take some enamelled copper wire, very thin but not critically so. Vero wire is ideal. Make off the end of the wire on the DIL socket end first and then trim the wire to length. With the end of the wire and the end of the pin both pretinned, and a clean tinned iron, solder the wire to the pin (and in one case, to the resistor lead). The best order is 7, 9, 25, 20, and 8. Pins 13-17 are not connected.
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Split
Figure 9. Keypad Overlay for Reproduction, 47 mm Wide by 57.5 mm High
It is traditional to drive 16 character backlit LCD displays in this sort of application. The cost would be comparable (for a one-off), power consumption noticeably less and the software complexity about the same, albeit totally different in nature. I preferred the LED approach since I find the LCD character size just a little small for comfortable viewing. The display digits are multiplexed that is, only one digit is lit at any one time, and all are lit in turn (rapidly and frequently) to provide flicker-free viewing. The software controls the multiplexing process and devotes as much time to repainting the display as circumstances permit. In operation, IC12 decodes RA0, 1, 2 to determine which one digit is being addressed-driving one of the PNP switches Tr5-Tr10 to handle the digit current. At the same time, IC11 decodes a BCD input on RB0, 1, 2, 3 to determine which segments to light and in addition RA3 is pulled low for a decimal point. By rushing round each digit in turn and by executing the entire sequence often enough, the human eye sees a continuous sixdigit display.
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Figure 10 shows the best way to achieve this. The cable is routed across the front of the display board beneath the frequency display and LEDs. It then passes behind the keypad and somewhat beyond it. The cable is then folded back on itself-i.e., through 180°-and then folded downwards through 90°. It is then made off onto the seven right-most pads on the keypad. This process produces a neat cable run with the correct connections. DISPLAY BOARD CONSTRUCTION NOTES The PCB layout is shown in Figure 12. The rear tracking is somewhat complex around the display IC sockets. A perfectly acceptable but less purist approach would be to bring these pins and those of IC11 out onto small pads and then hand wire all the segments to the sevensegment decoder using Vero wire. Other common anode devices, including single-digit ICs and those with pins on the vertical edges could easily be substituted with simple changes to the PCB-or again, by using Vero wire. The status LEDs may be tacked onto the board but without shortening their leads for commissioning purposes. When inserting ICs or IC sockets onto the board with this form of PCB construction, insert them only far enough to give a useful tail on the back of the board. Specifically, avoid bridging tracks or earthling pins on the component side of the board via the shoulders on the pins.
DISPLAY BOARD
KEYPAD
Figure 10. Display board to keypad ribbon cable routing viewed from the front. Note that of the eight connectors on the keypad, the extreme left one is not connected.
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5V (FROM DDS BOARD) C40 100 F C41 100 F VDD 1 RB4 6 4 G1 G2A R35 14 2.2k R36 13 2.2k C34 10nF C35 10nF C36 10nF C37 10nF C38 10nF C39 10nF
TR5 BC327 TR6 BC327 R37 2.2k R38 2.2k TR7 BC327 TR8 BC327 R39 2.2k R40 2.2k
IC12 74LS138
3-TO-8 DECODER
G2B 7, 15 NOT CONNECTED 4 11
TR9 BC327 TR10 BC327
13 ANODE2
14 ANODE1
13 ANODE2
14 ANODE1
13 ANODE2
DIGITS 5&6 a2 11 b2 10 c2 d2 e2 8 6 5
RB0 RB1
FROM DDS BOARD
11 c BCD TO 10 7-SEG d DECODER / 9 6 DRIVER e D 15 f 4, 5 NOT CONNECTED 14 g 2 C VSS 8 D3
IC11 74LS47
RA3 1N4148
R49 470 R50 470 R51 470 R52 470 R53 470 R54 470 R55 470
RA0 RA1 RA2 RB0 RB1 RB2 RB3
TO 4x3 KEYPAD VIA 7-WAY RIBBON CABLE
IC13 4094
SERIAL IN PARALLEL OUT SHIFT REGISTER AND LATCH RB5 RB2 RB3 1 2 3 LATCH DATA CLOCK 9, 10 NOT CONNECTED
Figure 11. Display board circuit diagram. Note that the segments of all the display ICS (8, 9, 10) are wired in parallel except for some decimal points which are never used and which are not connected. The eight 3 mm status LEDs, D4-D11 are soldered on the display board, but physically mounted in holes in the front panel.
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REAR VIEW - (NONCOMPONENT SIDE) SHOWING REAR TRACK AND SOLDERING POINTS
FRONT VIEW - (COMPONENT SIDE) SHOWING FRONT TRACK AND SOLDERING POINTS
12V C15
IC1 R4 R3 C6 C5
C11 TC2 R6
C17 C23
C20 RFOUT
R33 R16 R15
DDS ASSY COMPRISING IC4, R9, R10, R18, C14 C4 R7 C12
R29 R27
TR1 L1 C2 C1 C30 TC1
IR DETECTOR IC5
TR3 R13 C10 C21 R11 R12
C27 L4
C25 L3
C24 C26
C29 X2 R22 IC3 TR4 D2 R23
C18 R21
SLOTTED DISC 51MM DIA D1 DIODE ANODE
DIRECTION
R30 R31 MCLR RB7 RB6 0V
IC2 C16
IC6 C19
R26 R25
6.1" x 2.75"
5V RA0 RA1 RA2 RA4 RA3 18MHz 15MHz 14MHz 29MHz 28MHz 24MHz 21MHz 10MHz 0V USE CW IF USE USB IF USE LSB IF 7MHz 3.5MHz 1.8MHz BROADBAND SPARE T / R (PTT LINE) RB1 RB2 RB3 RB0 RB5 0V
SHAFT CENTER LINE TUNING KNOB (NOMINALLY 1.75" DIA)
NB ALL TRACKS MARKED 0V ARE CONNECTED TO THE GROUND PLANE
LOGIC INTERFACE TO Tx / Rx
TOP VIEW - SHOWING COMPONENT LOCATION AND DRILLING TEMPLATE
Figure 12. Display board PCB drawn for production as described in the text. The ground plane is not shown since all of the board (both sides) is ground plane copper except where removed to let in the tracking. Holes on the front and rear track views shown as an "x" are not soldered on that side of the board. They should be lightly countersunk. Holes shown as an "o" are soldered to either the track or the ground plane. All holes are 0.7 mm dia. The front panel LEDs (D4-D11) are not shown. They solder to the pad and ground plane pairs in a horizontal line about half way up the rear view. Nine short wire links are shown as pecked lines on the rear view.
PULSE
PROGRAMMER INTERFACE ONLY
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C18 1nF
C1 1nF
C2 1nF
R1 100
IC1 78L08
R3 10k
C5 1nF
C33 100p R5 1k R6 C32 47p 220
TR1 2N2222A
R14 1k
T1 TR3 2N3866 C23 10nF R16 56
X1 110MHz
R4 10k
C31 47p
DISPLAY & KEYPAD
RB4 RA3
IC4 AD9850 PIC
R10 200 R9 100
R13 470 R15 56
PROGRAM INTERFACE
R19 560 D1 LD271
Figure 13. DDS board circuit diagram. IC4 and its associated components are mounted on a 28-pin DIL socket to form the DDS assembly. This plugs into a 28-pin socket on the main board.
IC6 4094
LATCH Q5 Q6 Q7 Q8 Q2 9, 10 NOT CONNECTED VSS 8 5V 16 15 OSC2 RB2 17 RA0 18 RA1 RA2 VSS 5 RB1 1 1 LATCH R26 270k C30 15p VDD 15 OE Q1 4 10MHz Tx / Rx DIGITAL INTERFACE (OPTIONAL) Q3 Q4 14 BROADBAND 13 12 11 5 6 7 1.8MHz 3.5MHz 7.0MHz USE LSB IF USE USB IF USE CW IF
IC3 16C84 PIC
D2 IN4148 R23 1k TR4 BC108
1 IC5 HLC2705 DIRECTION IR 4 DETECTOR PULSES R21 1k 3 SLOTTED DISK 5V
R22 4.7k
SERIAL IN PARALLEL MUST DATA SHIFT REGISTER CLOCK & LATCH
PTT LINE FROM Tx / Rx
R32 4.7k
R24 270k
R25 270k
IC6 4094
Q5 Q6 Q7 Q8 Q2 9, 10 NOT CONNECTED VSS 8 Q3 Q4
21MHz 24MHz 28MHz 29MHz 14MHz 15MHz 18MHz
DISPLAY AND KEYPAD
SERIAL IN PARALLEL 2 MUST DATA SHIFT REGISTER 3 CLOCK & LATCH
RB1 RB2 RB3 RB0 RB6
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BOTTOM VIEW - (NON-COMPONENT SIDE) SHOWING BOTTOM TRACK AND SOLDERING POINTS
TOP VIEW - (COMPONENT SIDE) SHOWING TOP TRACK AND SOLDERING POINTS
12V C15
IC1 R4 R3 C6 C5
C11 TC2 R6
C17 C23
C20 RFOUT
R33 R16 R15
DDS ASSY COMPRISING IC4, R9, R10, R18, C14 C4 R7 C12
R29 R27
TR1 L1 C2 C1 C30 TC1
IR DETECTOR IC5
TR3 R13 C10 C21 R11 R12
C27 L4
C25 L3
C24 C26
C29 X2 R22 IC3 TR4 D2 R23
C18 R21
SLOTTED DISC 51MM DIA D1 DIODE ANODE
DIRECTION
R30 R31 MCLR RB7 RB6 0V
IC2 C16
IC6 C19
R26 R25
6.1" x 2.75"
5V RA0 RA1 RA2 RA4 RA3 18MHz 15MHz 14MHz 29MHz 28MHz 24MHz 21MHz 10MHz 0V USE CW IF USE USB IF USE LSB IF 7MHz 3.5MHz 1.8MHz BROADBAND SPARE T / R (PTT LINE) RB1 RB2 RB3 RB0 RB5 0V
SHAFT CENTER LINE TUNING KNOB (NOMINALLY 1.75" DIA)
NB ALL TRACKS MARKED 0V ARE CONNECTED TO THE GROUND PLANE
LOGIC INTERFACE TO Tx / Rx
TOP VIEW - SHOWING COMPONENT LOCATION AND DRILLING TEMPLATE
Figure 14. DDS board PCB drawn for production using same conventions as Figure 12. All holes are 0.7 mm dia except three leads from IC2 which are 1 mm. Ref oscillator is screened by PCB enclosure. C7 uses its leads to connect from tap on L2, via hold in enclosure to top track. C1 is connected to track via short jumpers. IR detector / diode and disc shown for mounting at 90 degrees to display to top track. C1 is connected to track via short jumpers. IR detector / diode and disc shown for mounting at 90 degrees to display board.
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PROGRAMMER INTERFACE ONLY
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Table I. Summary of Two-Key Entries First Key Second Key 0 1 2 3 4 5 6 7 8 9 Scan VFOs 9 15 m 9 160 m 9 17 m Flywheel Disable 9 Cal Down 1 kHz LSB Offset Scan Freq 1 USB 9 10 m Select USB 9 12 m Tune Rate Mode 9 Cal Ref Clock 9 Cal CW Offset Select CW Guard Channel Scan Memories 2 Rate 9 20 m 3 Cal 9 30 m 9 Cal USB offset 4 CW 9 40 m Up 1 kHz 5 Scan 6 Mem 9 Mem 0 9 Mem 1 9 Mem 2 9 Mem 3 9 Mem 4 9 Mem 5 9 Mem 6 9 Mem 7 9 Mem 8 9 Mem 9 Select LSB Shift Display Lo Side Injection Keypad Freq Entry Broad Band Sleep Mode Sig Gen Mode 7 LSB Bar Graph on Tune 8 Freq 9 80 m Hi Side Injection
E3732-.5-4 / 00 (rev. 0) PRINTED IN U.S.A.
Note that the ergonomic beauty of the entries can only be visualized when looking at the keypad layout with overlay legends. Entries shown preceded with a "9" save the current frequency in that location when the two-key entry is preceded by the "Save" 9 key. Other combinations are "990" which saves the power-on frequency and "999" which restarts the software.
Figure 15. 180 slot encoder disc, 51 mm dia for reproduction on acetate film.
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