12

®

OPA2658

DIFFERENTIAL GAIN AND PHASE

Differential Gain (dG) and Differential Phase (dP) are among

the more important specifications for video applications. dG

is defined as the percent change in closed-loop gain over a

specified change in output voltage level. dP is defined as the

change in degrees of the closed-loop phase over the same

output voltage change. Both dG and dP are specified at the

NTSC sub-carrier frequency of 3.58MHz and the PAL sub-

carrier of 4.43MHz. All NTSC measurements were per-

formed using a Tektronix model VM700A Video Measure-

ment Set.

dG/dP of the OPA2658 were measured with the amplifier in

a gain of +2V/V with 75

Ω input impedance and the output

back-terminated in 75

Ω. The input signal selected from the

generator was a 0V to 1.4V modulated ramp with sync pulse.

With these conditions the test circuit shown in Figure 9

delivered a 100IRE modulated ramp to the 75

Ω input of the

video analyzer. The signal averaging feature of the analyzer

was used to establish a reference against which the perfor-

mance of the amplifier was measured. Signal averaging was

also used to measure the dg and dp of the test signal in order

to eliminate the generator’s contribution to measured ampli-

fier performance. Typical performance of the OPA2658 is

0.025% differential gain and 0.02

° differential phase to both

NTSC and PAL standards.

10

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

1M

10M

100M

1G

Frequency (MHz)

G = +2

FIGURE 8. Channel-to-Channel Crosstalk.

FIGURE 9. Configuration for Testing Differential Gain/Phase.

SPICE MODELS

Computer simulation using SPICE is often useful when

analyzing the performance of analog circuits and systems.

This is particularly true for Video and RF amplifier circuits

where parasitic capacitance and inductance can have a major

effect on circuit performance. SPICE models are available

on a disk from the Burr-Brown Applications Department.

DEMONSTRATION BOARDS

Demonstration boards are available for each OPA2658 pack-

age style. These boards implement a very low parasitic

layout that will produce the excellent frequency and pulse

responses shown in the Typical Performance Curves. For

each package style, the recommended demonstration board

is:

DEMONSTRATION BOARD

PACKAGE

PRODUCT

DEM-OPA265xP

8-Pin DIP

OPA2658P

DEM-OPA265xU

SO-8

OPA2658U

OPA2658UB

DEM-OPA26xxE

MSOP-8

OPA2658E

75

Ω

75

Ω

402

Ω

402

Ω

75

Ω

75

Ω

TEK TSG 130A

TEK VM700A

OPA2658

Contact your local Burr-Brown sales office or distributor to

order demonstration boards.

TYPICAL APPLICATION

FIGURE 10. Low Distortion Video Amplifier.

OPA2658

V

OUT

402

Ω

402

Ω

Video

Input

75

Ω

75

Ω

75

Ω Transmission Line

75

Ω

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