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| 1 ========================================== | |
| 2 HP3562A Dynamic Signal Analyzer - Part 3 | |
| 3 ========================================== | |
| 4 | |
| 5 :Author: David Douard | |
| 6 :Category: Electronics | |
| 7 :Tags: HP3562A, repair, test equipment, DSA | |
| 8 :series: HP 3562A | |
| 9 :series_index: 3 | |
| 10 | |
| 11 This is the part 3 of the series about my | |
| 12 `HP 3562A Digital Signal Analyzer <{filename}hp3562a.rst>`_, | |
| 13 quickly describing the Analog Section of the instrument. | |
| 14 | |
| 15 | |
| 16 Analog Section | |
| 17 ============== | |
| 18 | |
| 19 The analog section consist in 6 boards: | |
| 20 | |
| 21 - A30: Analog Source | |
| 22 - A31: Trigger | |
| 23 - A32, A34: Input ADCs | |
| 24 - A33, A35: Input | |
| 25 | |
| 26 Analog Source | |
| 27 ------------- | |
| 28 | |
| 29 .. image:: {filename}images/hp3562a/hp3562a_a30_block_diagram.png | |
| 30 | |
| 31 This board is mainly a DAC converting signal signal from the Digital | |
| 32 Source board (for sin waves). It also generates Pseudo Random Noise | |
| 33 and square waves (used for input calibration). | |
| 34 | |
| 35 The analog signal produced by the DAC is filtered by a 100kHz low pass | |
| 36 filter, then pass throught a step attenuator (5mV per step). The way | |
| 37 this is implemented is quite interesting: the analog signal from the | |
| 38 main DAC is used a reference voltage for a multiplying DAC. | |
| 39 | |
| 40 .. image:: {filename}images/hp3562a/a30_analog_source.jpg | |
| 41 | |
| 42 .. image:: {filename}images/hp3562a/a30_analog_source_dac.jpg | |
| 43 | |
| 44 Trigger | |
| 45 ------- | |
| 46 | |
| 47 A first section of this board produces the trigger signal (for A1 | |
| 48 Digital Source and A5 Digital Filter boards) from one of the 4 | |
| 49 possible trigger sources: external, channel 1, channel 2 and the | |
| 50 calibration. | |
| 51 | |
| 52 .. image:: {filename}images/hp3562a/trigger_level.png | |
| 53 | |
| 54 The trigger clock circuit produces the 20.48MHz clock using a | |
| 55 VCXO. From this signal are derived the 10.24MHz clock used by many | |
| 56 boards (A1, A4, A5, A6, A30, A32 and A34) and the 256kHz clock signal | |
| 57 used as internal sample signal. | |
| 58 | |
| 59 When an external clock is provided, a PLL is used to lock this | |
| 60 20.48MHz. The external signal can be 1, 2, 5 or the standard 10MHz. | |
| 61 | |
| 62 .. image:: {filename}images/hp3562a/trigger_clock.png | |
| 63 | |
| 64 .. image:: {filename}images/hp3562a/a31_trigger.jpg | |
| 65 | |
| 66 | |
| 67 Input ADC | |
| 68 --------- | |
| 69 | |
| 70 .. image:: {filename}images/hp3562a/hp3562a_a32_block_diagram.png | |
| 71 | |
| 72 | |
| 73 The ADC board converts analog data from the input board into 13-bits | |
| 74 serial data words. The Analog to Digital convertion is done in 2 | |
| 75 passes by a 8-bits ADC. At each digitilization step, the signal value | |
| 76 is frozen by a Track and Hold circuit. This frozen value is digitized | |
| 77 (with a 8-bit resolution), then the digitized value is substracted | |
| 78 from the input (hold) signal and the result is multiplied then | |
| 79 digitized a second time to produce the remaining 5-bits of resolution. | |
| 80 | |
| 81 .. image:: {filename}images/hp3562a/a32_input_adc.jpg | |
| 82 .. image:: {filename}images/hp3562a/a32_input_adc_bb.jpg | |
| 83 | |
| 84 | |
| 85 Input | |
| 86 ----- | |
| 87 | |
| 88 .. image:: {filename}images/hp3562a/hp3562a_a33_block_diagram.png | |
| 89 | |
| 90 The input assembly implements the voltage ranges and conditions the | |
| 91 input signal. It mostly consist in a pair switch attenuators (the | |
| 92 input is balanced), followed by a pair of amplifier/signal | |
| 93 conditionners. The balanced signal is then fed into a differential | |
| 94 amplifier followed by a amplifier and an attenuator. | |
| 95 | |
| 96 .. image:: {filename}images/hp3562a/a33_input.jpg | |
| 97 | |
| 98 | |
| 99 Next | |
| 100 ==== | |
| 101 | |
| 102 In the `next part <{filename}hp3562a_4.rst>`_, we will describe the | |
| 103 HP 1345A Digital Display used in the instrument. |
