Softrock Lite II 04_Operational Amplifiers
Operational Amplifiers Introduction
Theory of Operation
The low-level In-Phase (I) and Quadrature (Q) IF signals from the Mixer are sampled over capacitors C5 and C6.
The Opamp amplifies the I and Q signals by a factor 100 times on 160M, 80M and 40M bands and by about 500 times on 30M, 20M and 15M.
Higher gain and a low noise LT6231 Opamps are supplied for the three highest bands to compensate for additional loss due to 1/3 harmonic sampling and the fact that atmospheric noise is lower on these bands allowing for more sensistive receivers to be used.
Operational Amplifiers Schematic
(Resistor testpoints (hairpin, top, or left-hand lead) are marked with red dots)
(Click for Full Schematic)
(above schematic has clickable areas that can be used for navigation)
Operational Amplifiers Bill of Materials
Detailed Bill of Materials
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C07 | 4.7 uF 10% | 475 | Ceramic | Operational Amplifiers | ||
| [____ ] | C08 | band-specific | Operational Amplifiers | ||||
| [____ ] | C09 | band-specific | Operational Amplifiers | ||||
| [____ ] | R03 | 1 k 1/4W 1% | br-blk-blk-br-br
 | 1/4W | W-E | Operational Amplifiers | |
| [____ ] | R04 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | W-E | Operational Amplifiers | |
| [____ ] | R05 | 10 ohm 1/4W 1% | br-blk-blk-gl-br
 | 1/4W | E-W | Operational Amplifiers | |
| [____ ] | R06 | 10 ohm 1/4W 1% | br-blk-blk-gl-br
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | R07 | band-specific | S-N | Operational Amplifiers | |||
| [____ ] | R08 | band-specific | E-W | Operational Amplifiers | |||
| [____ ] | R09 | 100 1/6W 5% |
 | 1/6W | E-W | Operational Amplifiers | |
| [____ ] | R10 | 100 1/6W 5% |
| 1/6W | E-W | Operational Amplifiers | |
| [____ ] | U4 | band-specific | Operational Amplifiers |
Band Specific Items for 160m Band
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C08 | 1500 pF 10% | 152 | Ceramic | Operational Amplifiers | ||
| [____ ] | C09 | 1500 pF 10% | 152 | Ceramic | Operational Amplifiers | ||
| [____ ] | R07 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | S-N | Operational Amplifiers | |
| [____ ] | R08 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | U4 | TVL2462CD dual opamp | TVL2462CD
 | SOIC-8 | Operational Amplifiers |
Band Specific Items for 80m Band
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C08 | 1500 pF 10% | 152 | Ceramic | Operational Amplifiers | ||
| [____ ] | C09 | 1500 pF 10% | 152 | Ceramic | Operational Amplifiers | ||
| [____ ] | R07 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | S-N | Operational Amplifiers | |
| [____ ] | R08 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | U4 | TVL2462CD dual opamp | TVL2462CD
| SOIC-8 | Operational Amplifiers |
Band Specific Items for 40m Band
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C08 | 1500 pF 10% | 152 | Ceramic | (could be replaced with 1000 pF - code 102) | Operational Amplifiers | |
| [____ ] | C09 | 1500 pF 10% | 152 | Ceramic | (could be replaced with 1000 pF - code 102) | Operational Amplifiers | |
| [____ ] | R07 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | S-N | Operational Amplifiers | |
| [____ ] | R08 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | U4 | TVL2462CD dual opamp | TVL2462CD
| SOIC-8 | Operational Amplifiers |
Band Specific Items for 30m Band
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C08 | 220 pF 5% | 221 | Ceramic | Operational Amplifiers | ||
| [____ ] | C09 | 220 pF 5% | 221 | Ceramic | Operational Amplifiers | ||
| [____ ] | R07 | 4.99 k 1/4W 1% |
 | 1/4W | S-N | Operational Amplifiers | |
| [____ ] | R08 | 4.99 k 1/4W 1% |
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | U4 | LT6231 | LT6231
 | SOIC-8 | Operational Amplifiers |
Band Specific Items for 20m Band
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C08 | 220 pF 5% | 221 | Ceramic | Operational Amplifiers | ||
| [____ ] | C09 | 220 pF 5% | 221 | Ceramic | Operational Amplifiers | ||
| [____ ] | R07 | 4.99 k 1/4W 1% |
| 1/4W | S-N | Operational Amplifiers | |
| [____ ] | R08 | 4.99 k 1/4W 1% |
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | U4 | LT6231 | LT6231
| SOIC-8 | Operational Amplifiers |
Band Specific Items for 15m Band
| Check | Designation | Component | Marking | Category | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| [____ ] | C08 | 220 pF 5% | 221 | Ceramic | Operational Amplifiers | ||
| [____ ] | C09 | 220 pF 5% | 221 | Ceramic | Operational Amplifiers | ||
| [____ ] | R07 | 4.99 k 1/4W 1% |
| 1/4W | S-N | Operational Amplifiers | |
| [____ ] | R08 | 4.99 k 1/4W 1% |
| 1/4W | E-W | Operational Amplifiers | |
| [____ ] | U4 | LT6231 | LT6231
| SOIC-8 | Operational Amplifiers |
Operational Amplifiers Summary Build Notes
- Install OpAmp
- Install band-specific components
- Install remaining components
- Test the Stage
Operational Amplifiers Detailed Build Notes
Bottom of the Board
Install OpAmp
Install the band-specific operational amplifier to the bottomside of the board.
The lower bands (160m, 80m, and 40m) use the TTLV2462
The higher bands (30m, 20m, and 15m) use the LT6231.
- Orient U4 on its pads so that the pin 1 corner of the IC matches the small “1" (it also looks like a “0”) mark in the copper on the bottom side of the board. In general, pin 1 of an SOIC packaged IC is in the lower left corner of the package when the printing on the package top reads upright, from left to right.
- Tack-solder one corner pin of U4 and reheat the tacked pin as necessary to line up U4 on its pads properly.
- Double-check the orientation of U4 and the line up of the IC on its pads with magnification and good lighting. You do NOT want to install U4 oriented incorrectly. If all is well, carefully solder the rest of the leads to their pads.
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| [____ ] | U4 | band-specific |
Top of the Board
Install band-specific components
Install the band-specific capacitors and resistors.
See band-specific chart for values
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| [____ ] | C08 | band-specific | ||||
| [____ ] | C09 | band-specific | ||||
| [____ ] | R07 | band-specific | S-N | |||
| [____ ] | R08 | band-specific | E-W |
Install remaining components
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| [____ ] | C07 | 4.7 uF 10% | 475 | Ceramic | ||
| [____ ] | R03 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | W-E | |
| [____ ] | R04 | 1 k 1/4W 1% | br-blk-blk-br-br
| 1/4W | W-E | |
| [____ ] | R05 | 10 ohm 1/4W 1% | br-blk-blk-gl-br
| 1/4W | E-W | |
| [____ ] | R06 | 10 ohm 1/4W 1% | br-blk-blk-gl-br
| 1/4W | E-W | |
| [____ ] | R09 | 100 1/6W 5% |
| 1/6W | E-W | |
| [____ ] | R10 | 100 1/6W 5% |
| 1/6W | E-W |
Operational Amplifiers Completed Stage
Top of the Board
Bottom of the Board
Operational Amplifiers Testing
Warning
Test Setup
Take appropriate ESD precautions in these tests, since you will be working around the sensitive OpAmp ICVisual Check
Test Setup
Using very good lighting and magnification, carefully inspect the solder joints to identify bridges, cold joints, or poor contacts.
Pay especial attention to the joints on the OpAmp IC pins. If necessary, touch up the joints with your iron and/or some flux. Wick up any excess.
Current Draw
Test Setup
- In each test, the ammeter must be placed in series between the positive lead of the power source and the board's positive power-in "+" terminal.
- In one test there is also a 100 ohm resistor in the series "chain" as well.
- in the second test, the setup is the same except that the current-liminting resistor is removed
Apply 12 Vdc to the board for this test
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| With 100 ohm current-limiting resistor | mA | < 3 | 1.9 | _______ |
| Without current limiting resistor | mA | < 3 | 2.7 | _______ |
Voltage Tests
Test Setup
Measure the voltages with respect to ground for each of the pins of U4. Tage care to measure at the actual IC pin rather than the pad, so as to ensure you are measuring the PIN voltage
expected voltages are indicated in the table below:
- 5 V (range of 4.5 - 5.4)
- 2.5 V (approx 50% of the 5V rail value)
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| Pin 1 | Vdc | 2.5 | 2.46 | _______ |
| Pin 2 | Vdc | 2.5 | 2.46 | _______ |
| Pin 3 | Vdc | 2.5 | 2.46 | _______ |
| Pin 4 | Vdc | 0 | 0 | _______ |
| Pin 5 | Vdc | 2.5 | 2.46 | _______ |
| Pin 6 | Vdc | 2.5 | 2.46 | _______ |
| Pin 7 | Vdc | 2.5 | 2.46 | _______ |
| Pin 8 | Vdc | 5 | 4.94 | _______ |
Functional Test
Test Setup
You will test the DC gain of each of the op-amps by connecting resistors Rt) from each op-amp inverting input to circuit ground. This will introduce a test current equal to 2.5 / Rt which will be balanced by the current fed back from each op-amp's output through each feedback resistor, Rf (i.e., R7 or R8). Each op-amp output will increase in voltage by 2.5 * Rf/ Rt from the nominal DC level of 2.5 volts.
The value of the test resistor (Rt) will depend upon the OpAmp used in the circuit:
- For the TLV2462 (160m, 80m, or 40m kit), use a 2.2 k ohm Rt
- For the LT6231 (30m, 20m, or 15m kit), use a 10 k ohm Rt
- Power up the circuit and measure the voltage at pin 1 of the op-amp (hairpin of R8). It should be ~2.5 Vdc
- Power off and use clip leads to connect Rt between the hairpin of R6 and circuit ground. (This provides an input resistance(Ri) of 2.2 k ohms or 10 k ohms (depending on the band) to the op-amp).
- Power up and measure the voltage at the hairpin of R8. You should get:
- For the TLV2462, with Rt = 2.2k ohm and R7, R8 = 1 k ohm: ~3.6 Vdc
- For the LT6231, with Rt=10 k ohm and R7, R8=4.99 k ohm: ~3.75 Vdc.
- Remove Rt and the output voltage should go back to ~2.5 Vdc.
- Perform the same test for op-amp 2, substituting R5 for R6 and R7 for R8
An Excel spreadsheet with a calculator for this test is available for you to plug in your bridging resistor ohms (Rt) and your pin 1 or pin 7 normal voltages (Ebias) and predict the expected voltage when bridged (Eout).
Test Measurements
Testpoint Units Nominal Value Author's Yours R7 without Rt (all kits) Vdc 2.5 2.48 _______ R8 without Rt (all kits) Vdc 2.5 2.46 _______ R7 with Rt (160m, 80m or 40m kit) Vdc 3.6 3.61 _______ R8 with Rt (160m, 80m or 40m kit) Vdc 3.6 3.59 _______ R7 with Rt (30m, 20m, 15m kit) Vdc 3.8 n/a _______ R8 with Rt (30m, 20m, 15m kit) Vdc 3.8 n/a _______