i have to design and build a self contained battery powered CRO balance preamplifier, to add high sensitivity ranges to an oscilloscope. This will be useful for testing audio and RF equipment up to over 15 MHz. The unit must be housed in a shielded box, that is, a metal or metal lined box.
Specifications
1. Balanced inputs, so either input may be grounded and the signal applied to the other input.
2. Voltage gain = 100 ± 3%
3. Frequency response to be flat within 1 dB from 40 Hz to 15 MHz.
4. Input (single ended) impedance > 1 KΩ, input capacitance < 5pF.
5. Output impedance < 100Ω.
6. The amplifier should be capable of driving a 100Ω load (external) up to 2 volts peak-peak without any visible sine wave distortion.
7. Using this preamplifier on the 10mV/division CRO input range will boost the CRO sensitivity to 100 μV/division. Hence the project must be housed in a shielded box also containing the batteries, and care must be taken with the construction to avoid hum pickup, spurious oscillation, etc.
Components
The following components are allowed: (i) any passive components (ii) any discrete diodes (including zeners) or transistors, (iii) any voltage regulator ICs. No other ICs are allowed, including opamps.
i have used a differential amplifier connected to a cascade amplifier, i have done the simulations on multisim and i got the required specifications, however in real life its a different story, the main problem am getting is that my upper frequency response is no where near the required specs am getting about 300KHz but the required is 15MHz. Am currently using BC549 transistors. Any suggestions on how i could improve my upper frequency response will be greatly appreciated.
Specifications
1. Balanced inputs, so either input may be grounded and the signal applied to the other input.
2. Voltage gain = 100 ± 3%
3. Frequency response to be flat within 1 dB from 40 Hz to 15 MHz.
4. Input (single ended) impedance > 1 KΩ, input capacitance < 5pF.
5. Output impedance < 100Ω.
6. The amplifier should be capable of driving a 100Ω load (external) up to 2 volts peak-peak without any visible sine wave distortion.
7. Using this preamplifier on the 10mV/division CRO input range will boost the CRO sensitivity to 100 μV/division. Hence the project must be housed in a shielded box also containing the batteries, and care must be taken with the construction to avoid hum pickup, spurious oscillation, etc.
Components
The following components are allowed: (i) any passive components (ii) any discrete diodes (including zeners) or transistors, (iii) any voltage regulator ICs. No other ICs are allowed, including opamps.
i have used a differential amplifier connected to a cascade amplifier, i have done the simulations on multisim and i got the required specifications, however in real life its a different story, the main problem am getting is that my upper frequency response is no where near the required specs am getting about 300KHz but the required is 15MHz. Am currently using BC549 transistors. Any suggestions on how i could improve my upper frequency response will be greatly appreciated.