# Schematic Challenge – Week 2

Blog Post created by ErinEast on Mar 12, 2018

Prove yourself as an engineer! The Schematic Challenge is the perfect opportunity to test your skills. On March 12, 13, and 14, we will be posting a new schematic or problem-solving challenge. If you, as a community, are able to answer questions 4, 5, and 6 correctly by Thursday, March 15 at 11:59 PM MST, we will add three 1000 X-Series oscilloscopes to the overall Wave 2018 giveaway! Answers should be posted in a comment on the #SchematicChallenge posts on the Keysight Bench or RF Facebook pages. Work with your family, friends, coworkers, or fellow engineers in the Wave community to solve these problems. If you haven’t already, be sure to register for Wave 2018 at wave.keysight.com.

Question 4:

By Ryan Carlino

Status: SOLVED! (A=1 and B=2)

Given this circuit and assuming an ideal op-amp powered by +/-5V and ideal resistors, calculate the output voltage with respect to the input. Vin will be limited to +/-1V.

Express this transfer function like this:
Vout = A*Vin + B

The answer being posted should be a single number AB. For example, if A=4 and B=7, the answer you should post is 47.

Question 5:

By Jonathan Falco and Lukas Mead

Status: SOLVED! (90 MHz)

What integer frequency in MHz should the LO be set, to allow the RF input range to be seen on OUT?

.

Question 6:

By Barrett Poe

Status: SOLVED! (4-10-8-8)

You are asked to design the front end of a 10 MHz oscilloscope. The “front end” refers to the internals of an oscilloscope between the probe and the analog to digital converter. Your system requires you take a +/- 10V signal input, and output a 0-3.3V signal to the ADC input, which is terminated at 50 Ohms. Your circuit must scale, offset, and filter the incoming signal, then rescale it to the full range (within 10%) of the ADC’s reference voltage without clipping the sampled signal.

Oh no! You also just discovered your supplier has discontinued your favorite ideal operational amplifier (opamp). Your next two best choices are:

• Opamp with 1 pF of capacitance on the inputs
• Opamp with 10 pF of capacitance on the inputs

Make sure your design works with both of these back-up options. However, note that you will only use the same parts together. Meaning, you will only ever have two 1 pF opamps OR two 10 pF opamps, never one of each.

Also keep in mind – opamp output voltage cannot exceed the supply rails.

Output Voltage = 0 to 3.3V; Ensure Vout is +0%/-10% of ADC range for max input across bandwidth

Frequency = DC to 10 MHz

Assign a value to variables a, b, c, and d. The final answer to be posted on Facebook should be expressed as: a-b-c-d. For example, if a = 8, b = 6, c = 12, and d = 10, then the answer should be expressed as: 8-6-12-10.

HINTS:

The variable “a” is equal to one of these three options

• c-1
• 4
• 4b

The variable “b” is equal to one of these three options

• c+1
• 4
• 10

The variable “c” is equal to one of these three options

• b/2
• 6
• 2*a

The variable “d” is equal to one of these three options

• 8
• (b+2)/3
• 10