思科2018校招硬件测试笔试试题及答案

(1/40) Which is the Thevenin equivalent for the circuit below?

A VO=49+8I

B VO=49-8I

C VO=25-8I

D VO=25-6I

正确答案：B

(2/40) The circuit below is used for:

Alow pass filter

Bhigh pass filter

Cband pass filter

Dband stop filter

正确答案：A

(3/40) For the following circuitry, assuming the driver is outputting 2.5V, Vin is 5V, Vgs(th) is 1.5V and R is 1M ohm, where is the FET’s quiescent point (Q-point) location?

ACut-off region

BTriode region

CSaturation region

DPre-pinch off region

正确答案：C

(4/40) Given the following design, which one is the correct waveform for output Y?

正确答案：C

(5/40) Which of the following terminology is not for the PCIE?

AInterrupt signal

BReceiver detection

CGen-2 5Gbps speed

DMax x16 lanes

EACK/NACK message

正确答案：A

(6/40) The passive probe is the most widely used general-purpose probe. The diagram below is the compensated attenuator in a probe with attenuation X10, what is the value of the C ideally?

A1pF

B9pF

C18pF

D2pF

正确答案：D

(7/40) Which of the following circuitry is perfectly diff-signal termination designed?

正确答案：A

(8/40) The following diagram shows the input and output structure of which type of interface?

ALVPECL

BLVDS

CCML

DCMOS

正确答案：C

(9/40) For the following I2C timing diagram, which statement is correct?

ASTART condition is not correct

BThis is a I2C read operation

CSlave address is “0101101”

DSTOP condition is not correct

正确答案：D

(10/40) In the memory test program, we wrote an inverted pattern into SRAM on 16 locations starting from location 0. After read it back, we found the pattern does not match what we wrote. Which of the following statement is true?

AThe address bit 0 is stuck at fault; The data bit 2 is stuck at fault

BThe address bit 1 is stuck at fault; The data bit 3 is stuck at fault

CThe address bit 2 is stuck at fault; The data bit 0 is stuck at fault

DThe address bit 3 is stuck at fault; The data bit 1 is stuck at fault

正确答案：B

(11/40) In the following circuit, the frequency at the output

Ahalf the input frequency

Bsame as input frequency

Ctwice the input frequency

Dfour times the input frequency

正确答案：C

(12/40) There are four popular DC-DC converters topology below, which one is the boost (step up) topology converter?

正确答案：B

(13/40) Which ones of the following are NOT common methods to reduce EMI when routing high speed signal:

AKeep consecutive reference plane for the signal trace, don't cross difference power plane.

BIncrease trace width

CWhen signal trace changes layer, place some vias or bypass capacitors that connect to power or ground plane

DReduce the loop area of returning current

正确答案：B

(14/40) Which kind of crystal oscillator has the best stability?

AXO

BVCXO

CTCXO

DOCXO

正确答案：D

(15/40) Two capacitors are connected in parallel through a switch. C1= 1uF, C2= 0.25uF. Initially switch is open, C1 is charged to 10V and C2 is not charged. What‘s the final voltage of C1 if we close the switch? Assume there is no loss in the wires and capacitors.

编辑

A2V

B1.25V

C8V

D5V

正确答案：C

(16/40) Under which corner condition does CMOS IC behave slowest?

AHigher temperature and higher voltage

BHigher temperature and lower voltage

CLower temperature and higher voltage

DLower temperature and lower voltage

正确答案：B

(17/40) Which of the following terminology is not for the SDRAM?

ACAS Latency

BPre-charge

CRetry

DRefresh

正确答案：C

(18/40) Regarding below circuit, Tsetup=Thold=Tco=1ns, Buffer delay is 2ns. Combinational logic delay is 3ns.

If use external logic to drive the circuit, what’s the setup time/hold time requirement for “data” signal?

A1ns/1ns

B-1ns/3ns

C0ns/2ns

D3ns/-1ns

正确答案：B

(19/40) Regarding the circuit in the above question, what’s the max frequency that the circuit can run?

A500MHz

B250MHz

C333MHz

D200MHz

正确答案：C

(20/40) Which one is the correct circuit after synthesis for below Verilog code?

always@(posedge clk or posedge rst) begin

if(rst) begin

o <= 1’b0;

end else begin

o <= a && b;

end

正确答案：B

(21/40) If you want to design an asynchronous FIFO with a dual port RAM. The FIFO width is 32bit, the depth is 16. If you can only use 4bit read/write address width, which kind of read/write address encoding is best?

Abinary coded decimal code

Bgrey code

Cone hot code

Dnone of above

正确答案：B

(22/40) The following figure is one async design. The data1_vld signal has enough pulse width and the data1[7:0] value will be kept unchanged within the pulse to assure we can get the data and one cycle pulse in clk2 domain. What problem do you see?

AIt is not necessary to synchronize data2[7:0].

Bdata2_vld is not a one cycle pulse.

Cdata2[7:0] and data2_vld do not need two flops to be synchronized to clk2 domain.

DI don’t see any problem.

正确答案：A

(23/40) Use a look-up table to design a FSM. The FSM has 25 states totally and 5 input control signals, what is the min size of look-up table to implement the FSM?

Athe look-up table is 30-bit address, 8-bit data

Bthe look-up table is 10-bit address, 5-bit data

Cthe look-up table is 10-bit address, 10-bit data

Dthe look-up table is 30-bit address, 5-bit data

正确答案：B

(24/40) Which one of below statements is correct?

AFPGA is a logic device using Product-Term structure

BThere’s no difference to connect the global clock to any FPGA user IO

C4 port input Look-up-table(LUT) can be implemented by 16x1 RAM

DFPGA device which use SRAM technology do not need to be configured after power on

正确答案：C

(25/40) In below circuit, clk is 10MHz. Suppose clear signal is synchronous with clk. When 1s after release clear signal, what’s the output of [Q2, Q1]?

A[00]

B[01]

C[10]

D[11]

正确答案：C

(26/40) Which of the following methods would increase the characteristic impedance of a microstrip line?

(1) Increase height of dielectric substrate h
(2) Decrease height of dielectric substrate h
(3) Increase trace width w
(4) Decrease trace width w
(5) Reduce permittivity of the substrate
(6) Increase permittivity of the substrate

A(2)(4)(5)

B(1)(3)(6)

C(1)(3)(5)

D(1)(4)(5)

正确答案：D

(27/40) If there is a signal with rise time 50 psec transmitting through an interconnector, and the 3dB bandwidth of the interconnector is 7GHz, how much is the rise time of the transmitted signal? (T rise time=0.35/BW)

A100 psec

B83.5 psec

C70.7 psec

D50.6 psec

正确答案：C

(28/40) Which expression is correct about crosstalk?

(1). The far-end crosstalk could be reduced by increasing the spacing between the signal traces.
(2). The total time the near-end noise lasts is 2 x TD. (TD: The time delay of the coupled) lines)
(3). The total time the near-end noise lasts is TD.
(4). No far-end crosstalk appears until a TD after the signal is launched.
(5). No far-end crosstalk appears until a 2 x TD after the signal is launched.

A(1)(2)(4)

B(1)(3)(5)

C(2)(4)

D(3)(5)

正确答案：A

(29/40) If you have a 6 layers stackup as below, Which layer is the best for high speed signal layout considering signal integrity and EMC?

ASignal 1

BSignal 2

CSignal 3

DSignal 4

正确答案：C

(30/40) The impedance of the channel could be measured by TDR (time domain reflectometer). Now there is a channel including transmission line, capacity and inductor. Which waveform will you see in the TDR?

正确答案：C

(31/40) If there is a signal transmitting from one layer to anther through via as shown in Figure (a), you will see a sharp dip at 10GHz from the measured insertion loss result shown in Figure (b). Please estimate the length of the stub?

A7.5mm

B10mm

C15mm

D30mm

正确答案：A

(32/40) Compare the transmission velocity in microstrip (v1), buried microstrip (v2) and stripline (v3) which have the same dielectric constant. Which relationship bellow is correct?

Av1=v2=v3

Bv1<v2<v3

Cv1>v2>v3

Dv1>v3>v2

正确答案：C

(33/40) The coupled lines have the odd-mode impedance (Zodd), even-mode impedance (Zeven), differential impedance (Zdiff) and common impedance (Zcomn). Which relationship is right?编辑

AZodd=Zdiff,Zeven=Zcomn

BZodd=Zdiff/2,Zeven=2*Zcomn

CZodd=2*Zdiff, Zeven=Zcomn/2

DZodd=Zdiff/2, Zeven=Zcomn/2

正确答案：B

(34/40) Which is the best layout for discrete decoupling caps of dc power?

正确答案：B

(35/40) The bellow figure is transmission line circuit. The time needed to transmit through the line is T. What is the voltage of point A at t=2T?

A2.5v

B2V

C1.2V

D2.2V

正确答案：B

(36/40) Which one or more of the followings properly describes random jitters:

Aexhibits Gaussian distribution

Bis a part of deterministic jitter

Cis linearly additive

Dis characterized by its bounded, peak-to-peak value

正确答案：A

(37/40) Choose WRONG approach about how to reduce probe to affect your measurement

AUse a probe with higher impedance

BProbe the signal somewhere else in the circuit at a test Point that has lower impedance.

CChoose a probe with bigger tip cap parameter

DChoose a probe with 5 time bandwidth than measured signal

正确答案：C

(38/40) The inductance per unit length and capacitance per unit length of a lossless transmission line are 0.405nH and 0.2pF respectively. What is the characteristic impedance of this transmission line?

A40ohm

B45ohm

C50ohm

D55ohm

正确答案：B

(39/40) Which of the following factors determine the bandwidth of signal?

Arise time

Bcycle time

Cclock jitter

Dflight time

正确答案：A

(40/40) In multilayer board, through hole via structure NOT include:

APad in positive layer

BPastemask in outer layer

CThermal pad or anti-pad in negative layer

DDrill hole and plated wall of hole

正确答案：B